What	Was	Molyneux's	Question	a	Question	About? Jonathan	Cohen	(University	of	California,	San	Diego) and Mohan	Matthen	(University	of	Toronto)1 Nearly	nine	hundred	years	ago,	the	Andalusian	Muslim	statesman	and	philosopher, Abu	Bakr	ibn	Tufail	(1105-1185),	conjectured	that	all	sensory	qualities	were	material,	and inferred	from	this	that	they	would	have	at	least	some	characteristics	that	can	be	discerned independently of sensory experience. Thus, he said, if a newly sighted	man encountered colours	for	the	first	time,	he	would	experience	them	in	ways	consonant	with	(at	least	some) descriptions of colours he had been given while still unsighted. Or perhaps he meant something	stronger,	namely	that	the	newly	sighted	man	could	actually	recognize	the	colours on	the	basis	of	the	descriptions	he	had	been	given	while	still	unsighted.2	Of	course,	on	either interpretation,	ibn	Tufail's	claim	is	controversial:	for,	granting	that	all	sensory	qualities	are material,	it	may	be	that	at	least	some	material	qualities	are	known	to	us	only	by	our	sensory experience	of	them-and	so	the	newly	sighted	man	might	have	no	prior	knowledge	on	which to	hang	the	descriptions	he	was	given	of	colour.	Nevertheless,	the	conjecture	prepares	us	for the	realization	that	some	material	qualities	might	not	be	available	to	any	sense,	and	others to	more	than	one. The	translation	of	ibn	Tufail's	book	into	Latin	by	Edward	Pococke	in	1671	sparked	a lively discussion of the empirical construction of concepts. (See Goodman, this volume.) William Molyneux pursued ibn Tufail's conjecture in a narrower and less controversial 1	This	is	a	fully	collaborative	work	of	the	two	authors. 2	In	this	formulation,	ibn	Tufail's	conjecture	concerning	colour	does	not	turn	on	amodal	or	inter-modal knowledge.	In	Lenn	Goodman's	translation	(this	volume),	the	crucial	passage	is Suppose	.	.	.	his	eyesight	were	restored	and	he	could	see.	He	would	walk	all	through	the	town	finding nothing	in	contradiction	to	what	he	had	believed,	nor	would	anything	look	wrong	to	him.	The	colors he	encountered	would	conform	to	the	guidelines	that	had	been	sketched	out	for	him. This leaves it open	whether or not visually	based "guidelines" could enable him, in	Molyneux's	words, to "distinguish	and	identify	by	sight	alone"	which	of	an	apple	and	a	leaf	was	red	and	which	was	green.	For	suppose he	had	been	told	something	like:	"Red	is	a	dark,	warm	colour	that	is	very	unlike	green,	which	is	bright	and	cool." C.L. Hardin's (1988) discussion of spectral inversion (ibid.	134-54) could be taken to imply that he	might actually	be	able	to	identify	red	and	green	on	this	basis.	If	so,	then,	perhaps	ibn	Tufail	was	right. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 2 form.3	Famously,	he	asked	Locke	(who	would	likely	have	recognized	the	allusion)	whether	a newly-sighted	man	could,	by	sight	alone,	distinguish	and	identify	a	globe	and	a	cube,	which he	previously knew	only by touch. This is a specific problem	about qualities that can	be sensed in more than one modality-Is there an inter-modally transferrable, or amodal, element	in	the	identification	of	three-dimensional	solids?	Though	derived	from	ibn	Tufail, this	question	leads	in	a	different	direction.	Our	purpose	here	is	to	ask	how	it	generalizes. What	was	the	theoretical	nerve	that	it	is	supposed	to	touch?	Why	is	it	so	revealing? The problem that guides us in this paper is	more pointed than	Molyneux's about sensory	knowledge in	a	newly	acquired	modality.	We	ask:	How	are ideas formed in	each modality,	and,	given	how	they	are	formed,	what	cross-modal	correspondences	can	we	expect to	find?	This	question	invites	a	more	granular	line	of	inquiry-one	that	takes	us	into	details of	the	construction	of	specific	qualities.	But	it	makes	ibn	Tufail's	conjecture	and	Molyneux's question	unexpectedly	relevant	to	a	number	of	unconnected,	but	familiar	problems	that	arise out of contemporary theorizing about perception. For, in contrast with many familiar approaches,	ours	poses	questions	about	cross-modal	divergence	and	convergence	that	range more	widely	than	those	envisaged	by	eighteenth	century	philosophers.	These	questions	are neutral	about	sensory	carry-over	of	the	kind	queried	by	Molyneux.4	In	short,	it	turns	out	that there	are	more	questions	and	more	answers	on	this	terrain	than	Molyneux,	Locke,	and	most of	their	successors	realized. I. On	the	origin	of	general	ideas Very	likely,	Molyneux	and	Locke	thought	of	the	question	like	this.	We	know	certain shapes	by	touch.	We	also	know	the	very	same	shapes	by	sight.	Consider,	then,	the	idea	of	a shape given to us by touch-the	mental representation of a shape that we arrive at by touching	it	("the	Object	of	the	Understanding	when	a	Man	thinks,"	as	Locke	puts	it).	Is	this the	same	as	the	idea	of	the	same	shape	given	to	us	by	sight?	Or	are	these	ideas	different?	To 3	Whether	he	came	across	the	topic	by	reading	ibn	Tufail	or	through	the	ensuing	discussion	is	not	clear. 4	In	fact,	one	way	that	our	approach	is	neutral	is	that	it	does	not	turn	on	any	particular	demarcation	of the	sense-modalities. In	Matthen	and	Cohen	(forthcoming),	we	even	note the	possibility	of	within-modality Molyneux	Questions. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 3 repeat:	these	questions	are	not	the	same	as	asking	whether	there	can	be	tactual	and	visual ideas	of	the	same	shape.	There	can	be	different	ideas	of	the	same	thing. Molyneux's	question	is	about	the	ability	to	identify	a	shape,	or	to	distinguish	it	from others.	Whether	or	not	he	and	Locke	were	clear	about it, this is	a	question	about	general ideas, i.e., ideas of repeatable types-Can the newly-sighted	man visually recognize this particular thing	here	as	an instance	of	a	general idea that	he	earlier	arrived	at	by tactual experience	of	other	things?	According	to	Locke,	a	general	idea	is	an	abstraction	created	by discarding	irrelevant	characteristics	of	particulars.	For	instance,	the	general	idea	of	a	triangle is	"neither	Oblique	nor	Rectangle,	neither	Equilateral,	Equicrural	nor	Scalenon;	but	all	and none	of	these	at	once."	(Essay	IV.vii.9)	The	question	Molyneux	poses	is	not	about	all	aspects of	visual	or	tactual	experience	of	globes	and	cubes.	A	particular	globe	might	look	red,	shiny, and	about	a foot	across;	at	the	same	time, it	might feel	cold,	dry,	and	about	a foot	across. Some of these attributes of the globe are purely visual, some purely tactual; one is (apparently)	shared.	None	of	them,	however,	are	essential	to	the	general,	repeatable	idea, GLOBE, as such;5 they are all discarded in the psychological act of generalization that terminates	in	that	general	idea.	This	invites	the	question:	What	qualities	are	retained	when a	blind	man	forms	a	general	idea	of	a	globe	from	his	tactual	experience? Now:	It	is	clear	that	in	at	least	some	cases,	one	can,	by	discarding	components	of	an idea originally experienced by touch, arrive at a residue is not specifically tactual-the general ideas THREE-DIMENSIONAL, SYMMETRICAL, EQUALLY SLOPED are examples of this.	So	when	we	consider	the	general	idea,	GLOBE,	formed	from	touch,	we	should	ask:	Are the retained qualities specifically tactual, or does the resultant general mental representation	subsume	the	visual	presentation	as	well,	as	a	presentation	of	the	very	same repeatable	type?	And	this	naturally	raises	the	question	whether	the	general	idea	that	results from	normal	visual	processing	is	the	same	or	different	in	content	from	the	idea	that	the	blind man	possesses. Molyneux's Question has sometimes been thought to be about the "differences between	the	qualitative	or	phenomenal	character"	of	visual	and	tactual	experiences	of	the 5	We	capitalize	terms	that	stand	for	ideas	and	italicize	those	that	stand	for	properties. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 4 same	thing	(see	e.g.,	Schwenkler	2019).	For	the	subjective	experience	of	exploring	a	globe	by touch	is	obviously	quite	different	from	that	of	examining	it	by	sight6-and	this	is	clearly	a relevant	consideration.	But	Molyneux's	Question	is	not	about	the	particular	experiences	that a	newly-sighted	man	suffers	when	he	looks	at	a	globe.	Rather,	it	is	about	this	man's	ability	to apply a general idea-i.e., a representation	of a repeatable	perceptual	property-that	he obtained	by touch	to	objects	newly	encountered in	visual	experience.	Since	general ideas omit certain features of particular experiences, we have to ask whether the retained characteristics	are	inter-modally	comparable.	In	other	words:	Can	the	subjectively	different experiences	of	the	same	shape	thrown	up	by	two	different	sense	modalities	be	subsumed under the same general idea, or at least general ideas that can be compared across phenomenal	differences? Locke	answered	Molyneux	negatively.	And	perhaps	he	did	so	because	he	was	not	alert (in	that	context)	to	how	vision	and	touch	can	arrive	at	the	same	general	ideas	by	discarding specifically	modal aspects of experience.7 But even if	we	disagree	with Locke about this, there	is	another	question	that	arises	for	anybody	who	was	inclined	to	think	that	general	ideas of	shape	are	cross-modally	comparable.	Allow	that	a	general	idea	arrived	at	by	touch	alone could	in	fact	be	the	same	in	content	as	that	arrived	at	by	vision.	We	still	do	not	know	whether it	is	equally	apt	to	be	applied	to	a	particular	idea	by	vision.	Take	the	idea	BOUNDED	OBJECT. This is clearly	an idea that	has	application in	more than	one	modality.	Yet, its	method	of application	might	differ	in	different	modalities:	specifically,	in	touch,	vision,	and	audition.	So, it could very	well be that a	newly sighted	man	might	be	hesitant in identifying	bounded objects	visually. Coming back to the general idea, GLOBE, the point to be emphasized here is that shared	content	is	not	the	only	question	of	interest	that	Molyneux	raised.	Concede,	in	other words,	that	there	is	only	one	general	idea	in	play,	or	that	there	are	two	but	with	significant cross-modal	structural	correspondences	of	content.	The	question	still	remains:	Can	one	just 6	But	see	Campbell	1996	(304),	who	thinks	(on	naïve	realist	grounds)	that	the	shape	itself	constitutes, indeed	individuates,	any	experience	of	it. 7	In	Essay	II	5,	Locke	writes,	"we can receive and convey into our minds the ideas of the extension, figure, motion, and rest of bodies, both by seeing and feeling." For	discussion	of	this	and	related	points,	see Matthen	and	Cohen,	forthcoming. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 5 as	easily	use	the	tactually	formed	idea	to	"distinguish	and	identify"	a	shape	as	a	globe	(rather than	a	cube)	when	looking	at	it	as	when	touching	it?	And:	Is	the	perceptual	process	by	which retained	qualities	are	identified	analogous	or	different? II.	Experience,	ideas,	and	properties When addressing Molyneux's Question, one can ask about at least four different contrasts	between	visual	and	haptic	perception. (1)	Experience	of	seeing	a	globe	vs	experience	of	feeling	it	by	touch. (2)	Idea	generalized	from	visual	experience	vs	idea	generalized	from	touch. (3)	The	property	revealed	by	vision	vs	the	property	revealed	by	touch. (4)	The	ability	to	re-identify	by	vision	the	property	revealed	by	touch. Much	of the	philosophical	dialectic	regarding	MQ	revolves	around	the	connections among	the	first	three	contrasts.	We'll	follow	this	dialectic	for	the	most	part,	though	we	will make	mention	of	the	additional	contrasts	with	(4). On	one	hand,	it is	clear	that	the	experiences	(1)	are	different.	Some	are	inclined	to think	that	this	settles	the	question	about	the	ideas,	(2). An	empiricist	might	argue	that	one cannot	erase the	sensory	source	of	one's	general ideas in the	relevant	cases. If so, then	a negative	answer	to	Molyneux's	Question	follows:	the	general	ideas	are	different. On	the	other	hand,	sphere	is	a	geometric	or	spatial	property	that	entails	qualities	such as	symmetry	and	roundness.	Some	writers	(e.g.,	Bennett,	1965,	and	Evans,	1985)	hold	that these qualities are inter-modally comparable. According to them, there is no relevant difference between the items in (3). And this, they think, settles, or at least severely constrains,	the	question	about	ideas-SPHERE	must	be	the	same	general	idea	across	vision and	touch,	or	at	least	structurally	similar	enough	to	distinguish	it	from	CUBE. Both	sides	err	by	neglecting	the	bridge	from	their	starting	point	to	the	middle	term- that	middle	term	being	(2)	general	ideas.	For	both,	the	question	is:	Is	sensory	experience	of a geometrical solid sufficient to form	a	modality-neutral subjective representation	of the solid?	An	empiricist like	Locke	answers 'No'	because	of the	difference in	the	experiences; Bennett and Evans answer 'Yes' because of the alleged non-modality of the sensed WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 6 properties.	But	it's	not	clear	exactly	where	the	answer	turns	from	negative	to	positive	when we go from (1) to (3). As against Locke, there's the possibility that all tactually specific dimensions	of	the	idea	are	bleached	out	by	the	generalization	process	before	we	get	to	(2). As	against	Bennett	and	Evans,	there's	the	possibility	that	even	if	our	ideas	of	shape	represent an	amodal,	or	intermodally	comparable,	property,	the	general ideas	formed	from	modally specific	experience	are	sufficiently	tainted	by	their	modal	origins	as	to	be	not	only	distinct, but	also	difficult,	or	even	impossible,	to	apply	in	vision	when	they	originate	in	touch. This sort of question can be asked about other general ideas as	well. Ibn Tufail's conjecture was that colour could be known (at least descriptively) by touch. This is implausible, because colour is a specifically visual idea (but see	note	2 above).	But	what about	other	features	known	by	more	than	one	sense?	Not	all	of	these	are	shapes;	indeed,	not all	are	spatial.	For	instance,	what	about	number?	If	the	newly-sighted	man	were	shown	one globe	on	his	left	and	two	on	his	right,	could	he	distinguish	and	identify	the	cardinality	of	the two	collections	by	sight	alone?	And	(as	Gareth	Evans	asked)	what	about	temporally	extended experiences:	if	the	newly	sighted	man	were	shown	a	steady	light	on	the	left	and	a	pulsating one	on	the	right,	could	he	tell	which	was	which?	One	could	ask:	is	there	a	general	recipe	for answering	questions	of	this	sort?	Given	that	we	don't	know	in	advance	what	will	be	omitted in	any	given	process	of	generalization,	it	doesn't	seem	that	there	could	be. In	earlier	work	(Matthen	and	Cohen	forthcoming),	we	argued	that	though	a	negative answer is warranted in a wide variety of cases, this conclusion can only be reached empirically	and	piecemeal.	Both	empiricists	like	Locke	and	their	opponents	like	Evans	are wrong	to	treat	Molyneux's	Question	as	a	single	question	about	the	origin	of	ideas	in	different modalities.8	Rather,	it	is	properly	posed	as	a	question	about	specific	ideas	in	specific	contexts. Thus,	we posited "Many	Molyneux	Questions," and argued for a classificatory scheme of these by the spatiotemporal dimensionality of the property represented by the idea in question. In	this	paper,	we	venture	beyond	this	conclusion	in	three	ways. 8	Cf.	Glenney	2013. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 7 We argue, first (sections III-V), that in each modality, complex ideas may differ structurally	from	the	corresponding	property.	This	sheds	light	on	how	(contrary	to the	conclusions	of	Gareth	Evans)	non-correspondent	ideas	of	the	same	shape	might be	constructed	from	an	inter-modally	shared	representation	of	space.	In	these	cases, the answer to Molyneux's Question is No: the newly sighted man does not have anything	on	which	to	base	visual	identification. Second, we show (sections VI-VII) that in certain cases, different modalities contingently	construct	structurally	correspondent	ideas	of	shapeand	space-related properties. In these	cases,	we	get	a	somewhat	surprising	Yes, if	not to	Molyneux's Question	as	posed,	then	at	least	to	the	question	whether	there	are	significant	crossmodal correspondences. (Of particular interest in this argument: the "new" modalities	created	by	sensory	substitution.) Finally	(section	VIII),	we	ask	(but	leave	unanswered)	new	questions	in	the	style	of	ibn Tufail	and	Molyneux	regarding	a	significant	class	of	non-spatial	ideas,	namely	those involved	in	evaluative	perception	and	perceptual	affect. III.	A	New	Question:	Analyzing	ideas Let's	now	consider	a	different	path	into	Molyneux's	Question,	similar	in	some	ways	to the	one	originally	explored	by	Denis	Diderot	(1749/1951)	and	discussed	by	Gareth	Evans (1985).	Locke	distinguishes	between	simple	and	complex ideas. Simple ideas	are	not	put together	from	other	ideas;	complex	ideas	are.	For	any	complex	idea,	one	can	ask:	How	is	it constructed	from	simples?	Now,	suppose	(as	many	philosophers	have)	that	the	simple	ideas of touch	and	vision	are	always	point-located	qualities.9	Then, it	would follow that shapeideas,	such	as	GLOBE	and	CUBE,	which	are	about	spatial	distributions	of	points,	are	complex. So,	if	one	could	establish	that	the	process	of	constructing	the	idea	SPHERE	from	point-located qualities	is	structurally	different	in	touch	and	in	vision,	this	would	give	us	reason	for	thinking that	this	idea	is	modally	specific. To	start	with,	the	question	whether	a	newly	sighted	man	is	able	to	recognize	a	tactual complex idea	without using touch is different from the question whether he is able to 9	This	is	the	assumption	of	the	colour	mosaic	theory	sketched	by	Lewis	1966. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 8 recognize	it	by	vision.	For	consider	the	complex	idea,	RS=ROUND	AND	STATIONARY.	Hold	in abeyance	the	question	whether	the	newly	sighted	man	would	visually	be	able	to	identify	the simple ideas,	ROUND	and	STATIONARY.	Allow	this	man	whatever time	and	experience is sufficient	to	learn	these	ideas.	And	now	put	the	question:	what	more	would	it	take	for	him	to be	able	to	identify	instances	of	RS?	Presumably	nothing	more.	AND	is	an	analytic	operation, and therefore	not	one	whose	acquisition	depends	on	sensory	experiences that the	newly sighted	man	might	be thought to lack.	So, it is	extremely	plausible to think	that	he	needs nothing	more	to	learn	RS	than	how	to	identify	its	simple	components.	But	this	argument	does not	show	that	RS	can	be	applied	visually.	Of	course,	we	have	reason	for	believing	that	the conjunctive	idea	AND	is	deployed	in	cognition.	But	it	is	a	substantive	empirical	question,	not something	that	can	simply	be	taken	for	granted,	that	AND	can	be	applied	straightforwardly in	the	construction	and	deployment	of	ideas	within	vision. Second,	note	also	that	one	cannot	safely	conclude	that	AND	is,	indeed,	applied	in	the formation	of	a	visual	idea	merely	from	the	fact	that	the	idea	picks	out	a	property	that	has	a conjunctive analysis. Some small animals preyed on by large birds have a distinctive behavioural	response	(they	freeze)	to	visually	detected	instances	of	the	conjunctive	property dark and looming (but not to visually detected instances of the property dark or of the property	looming).	Presumably	they	have	a	visual	representation/idea	of	(i.e.,	whose	content is) the complex, conjunctive property. But it does not follow that this idea is a complex construction	with	DARK,	LOOMING,	and	AND	as	constituents:	it	could	well	be	that	their	idea of	the	property	dark	and	looming	is	an	uncomposed	atom.	(As	an	aside:	this	would	cast	doubt on	the	notion	that	all	simple	ideas	are	point-located	qualities.) In	sum,	it	is	wrong	to	think that if	a	property	can	be	analysed	as	a	conjunction, then	the idea	of that	property	will	be conjunctive	(and	hence	complex).	The	logical	or	mathematical	structure	of	a	property	need not	be	reflected	in	the	structure	of	the	sensory	idea	of	that	property	(cf.	Hopkins,	2005). On	reflection,	it	seems	that	Diderot's	approach	to	Molyneux's	Question	also	leans	on an	analysis	of	the	property,	though	in	a	somewhat	different	way.	Diderot	famously	holds	that vision	and	touch	must	have	different	ways	of	apprehending	the	mathematical	structure	of shape-properties.	He	assumes	(mistakenly,	as	we	contend)	that	since	shape-properties	are spatial	distributions	of	points, shape ideas	must	also	be	constructed from	ideas	of	spatial WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 9 distributions.	He	reasons	that,	since	one	can	at	a	single	glance	form	an	impression	of	how spheres	look,	the	visual	idea	can	be	formed	by	a	simultaneous	apprehension	of	the	spatial relationships	of	constituent	points. In	contrast,	he	supposes that the tactual idea	of these relations	can	only	be	formed	by	a	temporally	extended	process:	one	cannot	apprehend	the whole	sphere	simultaneously	by	touch,	and	so	one	has	to	rely	on	moving	one's	hands	over	it. He	concludes	that	the	tactual	idea	of	a	sphere	is	different	from	the	visual	idea-the	former has	a	kind	of	temporal	structure	that	the	latter	lacks. But this line	of argument is	mistaken. It is true that	vision	and touch	differ in the spatial range over which they deliver information at a single instant. However, this is precisely the sort of difference that is put aside in the abstractive process that leads to general ideas.	For	consider: if	a	sphere is	sufficiently	small	relative	to	the	spatiotemporal range of vision then it can be visually apprehended at a moment, and one can then immediately	form	from	it	a	visually	generated	general	idea	of	sphericality.10	(In	this	process, one	discards	size	information,	inter	alia.)	And	exactly	the	same	is	true	of	touch:	if	a	sphere	is sufficiently	small	relative	to	the	spatiotemporal	range	of	touch,	one	can	apprehend	its	shape at	a	single	instant	and	form	from	it	a	haptically-generated	general	idea	of	sphericality	(which discards	size	information,	inter	alia).11 Of	course,	Diderot	is	right	that	if	the	sphere	is	too	large	to	be	haptically	apprehended at	a	time,	then	one	needs	to	engage	in	temporally	extended	haptic	exploration	to	form	from it	a	general	idea	of	sphericality.	But	the	same	is	true	of	vision,	with	the	difference	that	the spatiotemporal	extent	of	the	visual	glance	is	larger	than	that	of	touch.	But	this	is	irrelevant, given	that	size	information	is	discarded	when	we	form	the	idea,	SPHERE.	It	would	seem,	then, that,	with	respect	to	the	perceptual	acquisition	of	general	ideas,	the	modalities	of	vision	and touch	are	on	a	par:	Diderot's	alleged	structural	contrast	between	the	two	rests	entirely	on	a modal	difference in	spatiotemporal	range	that is	properly ignored	in	consideration	of	the perceptual	acquisition	of	general ideas.	He	simply	overlooks	the	possibility	that	a	general 10	See	Klatzky	and	Lederman	(1995)	on	the	haptic	glance. 11	In	neither	case	does	the	apprehension	at	issue	demand	perceptual	contact	with	all	of	the	points	in the	sphere;	rather,	what	is	required	is	presumably	just	the	sort	of	perceptual	contact	with	facing	surfaces	that supports	acquisition	of	a	general	shape	idea.	This	is	another	way	of	reinforcing	the	point	that	the	structure	of our	perceptually	derived	ideas	need	not	be	the	same	as	that	of	the	corresponding	properties. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 10 idea	of	SPHERE	could	be	constructed	from	an	experience	of	a	sphere	that	is	small	enough	to be	apprehended	at	an	instant,	whether	it	is	a	hand-size	sphere	apprehensible	by	touch	or	a much	larger	one	apprehensible	by	vision. Moreover,	and	even	putting	the	last	point	aside,	Diderot	neglects	the	possibility	that even	if	touch	apprehends	particular	spheres	temporally,	the	general	tactual	idea	of	a	sphere could	be	formed	by	discarding	temporality.	(Evans	gives	some	anecdotal	evidence	in	favour of	this	possibility.)	But	even	then,	it	would	not	follow	that	touch	and	sight	are	equally	adept at	making	the	comparison.	Even	if	both	modalities	have	a	non-temporal	idea,	they	might	have different ideas. Or they may have the same idea (or structurally comparable ones); nonetheless,	blind	subjects	may	still	not	be	able	to	make	the	cross-modal	comparison	in	a way	that	enables	them	immediately	to	visually	recognize	spheres	when	they	recover	sight. And,	as	a	matter	of	fact,	Pawan	Sinha	and	colleagues	report	empirical	evidence	that	indicates an inability of newly sighted people to recognize shapes (Held et. al. 2011; Ostrovsky, Andalman,	and	Sinha	2006;	Ostrovsky	et.	al	2009).	In	short,	we	have	no	grounds	for	a	general answer,	or	even	grounds	to	formulate	a	general	question. To	summarize	our	line	of	thought	in	this	section:	It	is	wrong	to	assume	that	a	sensory idea of a shape must reflect the analysis of the shape-property. A sphere is a certain distribution of points in space, but it doesn't follow that the visual idea of a shape is a representation just of that distribution-it may instead reflect gross characteristics distributed	across a surface, for example, a smooth lighting gradient	or a certain	kind	of textural	variation.	For	this	reason,	we	can't	assume	that	touch	and	vision	recognize	spheres in	the	same	way.	If	each	relies	on	clues	and	indications	rather	than	the	actual	geometrical analysis	of	a	sphere,	they	might	rely	on	different	cues.	Or	they	might	rely	on	comparable	cues (see	section	VI).	The	question	is	open. This	informs	our	general	approach	to	inter-modal	transfer:	the	question	has	to	be	put for	specific	ideas	of	specific	shapes,	and	not	for	whole	modalities.	Interestingly,	the	answers given by Locke,	Diderot, and	many contemporary philosophers (including	Gareth	Evans) follow	something	much	closer	to	a	whole-modality	strategy.	However,	we	suggest,	reflection on	Molyneux's	question	about	globes	and	cubes	motivates	a	finer-grained	approach. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 11 IV.	Space	and	the	Modalities:	Sceptical	Remarks On	its	face,	the	question	Molyneux	poses	is	about	shape.	But	Evans	attempts	to	reduce this to an issue about space-specifically, about "the relation between the perceptual representation	of	space	attributable	to	the	blind,	and	the	perceptual	representation	of	space available	in	visual	perception."	This	is	wrong	for	a	number	of	reasons.	The	shift	from	shape to space	occurs	against the	background	of	Diderot's argument.	As	we	have seen,	Diderot thought	that	the	blind	can	perceptually	register	shape	only	by	temporally	extended	tactile exploration,	and	that	their	idea	of	shape	is	therefore	that	of	a	process.	Evans	rightly	rejected this	argument. Evans is right to reject a facile inference from temporally extended experience of shape to temporally extended representation of space, but his critique does not touch Diderot.	For	a	follower	of	Diderot	could	concede	that	the	blind	operate	with	a	"simultaneous" conception of space when they are locating individual points, while still insisting that temporal-process	notions	have	to	be	collated	over	time	in	order	to	get	ideas	of	shape.	Nonsimultaneous shape-representations are compatible with an underlying simultaneous space-representations. More	significantly,	both	Diderot	and	Evans	overlook	the	fact	that	there	could	be	more than	one	way to	keep track	of	position (Tolman	1948,	O'Keefe	and	Nadel	1978,	Gallistel, 1990).	Some	animals	use	travel	metrics	("Walk	steadily for ten	minutes,	slow	down, turn right,	.	.	."	etc.)	to	measure	position,	as	inertial	navigation	systems	do.	This	doesn't	preclude them taking in spatial positions in a single glance. The test of whether an organism is sensitive	to	allocentric	spatial	layout	is	its	ability	to	get	from	C	to	A	after	first	going	from	A to	B	and	B	to	C,	where	A,	B,	and	C	are	not	collinear.	Similarly,	the	test	of	whether	it	represents an	object's	shape	is	its	ability	to	trace	the	shape	from	multiple	different	starting	points-top, bottom,	middle.	Touch	and	vision	might	be	able	to	keep	track	of	position	relative	to	a	starting point	without	employing the	same	pre-existing	representation	of space. In fact, there	are significant	structural	differences	between	touch	and	vision	regarding	how	they	represent space	(Matthen	forthcoming).	So,	coordinating	the	two	senses	is	not	straightforward. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 12 A	historical	aside.	Ibn	Tufail's	conjecture	about	the	newly	sighted	man	occurs	in	his story,	Haiy	ibn	Yaqzan,	which	is	a	philosophical	allegory	about	a	boy	cast	away	at	birth	on	an island.	Brought	up	by	a	gazelle,	and	utterly	deprived	of	human	contact,	this	boy	comes	to know	everything	that	advanced	cultures	know,	from	the	manufacture	of	clothing,	to	morals and religion, to cosmology. In the seventeenth century, this book was widely read, supposedly influencing	Spinoza,	Hobbes, and	Locke (independently	of	Molyneux's letter), and	inspiring	Defoe's	Robinson	Crusoe.	The	newly	sighted	man	is	a	thought	experiment	in	the Introduction	to	the	book;	it	elaborates	the	theme	of	knowledge	in	the	absence	of	exposure	to the	most	direct	sources	of	knowledge:	"Colours	were	such	as	he	had	before	conceiv'd	them to	be,	by	those	descriptions	he	had	receiv'd."	Molyneux	cleverly	plucked	this	anecdote	from the	book	(or	from	the	contemporary	discussion	surrounding	it)	and	sharpened	it.	But	since it	is	couched	in	such	specific	terms,	it	is	difficult	to	know	exactly	how	he	viewed	the	problem. Locke	himself	didn't	get	the	point	at	first	glance,	though	he	probably	knew	ibn	Tufail's	book. Presumably,	Molyneux intended to	query ibn	Tufail's theme	of	knowledge	without	direct experience.	Cross-modal	carry-over	isn't	the	only	consideration	relevant	to	this	theme,	nor (as	Evans	realized)	is	associative	learning	vs	innateness.	This	is	why	we	cast	the	net	wider. Given	this	historical	background,	it	is	entirely	possible	that	Molyneux	thought	about his problem about cross-modal comparisons and associations simply as an instance of a much wider puzzlement. You have all sorts of non-spatial perceptual ideas of familiar things-of	your	loved	ones,	of	the	place	where	you	live,	of	your	clothes,	and	so	on.	You	have many feelings evoked by perception: remember the terror induced in small animals by looming	shadows.	Are	these	non-spatial	ideas	transferrable	from	one	modality	to	another, or	comparable	between	them?	We'll	return	to	these	questions	below,	but	for	now	let's	just acknowledge	that	there	is	no	reason	to	think	that	Molyneux's	Question	was	ultimately	about just shape. (In fact, Molyneux's original formulation of the question to Locke explicitly invokes	distance:	"Or	Whether	he	Could	know	by	his	sight,	before	he	stretchd	out	his	Hand, whether	he	Could	not	Reach	them,	tho	they	were	Removed	20	or	1000	feet	from	him?")	And even if it was, there is, more importantly, no reason to think that it reduces without remainder	to	a	problem	about	the	representation	of	space. V.	Shape:	Foundation	and	Integration WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 13 Evans	holds	that	our	ideas	of	location	and/or	direction	are	shared	by	more	than	one modality.	Suppose	he	is	right.	Let	a	light	be	switched	on.	Can	a	newly	sighted	man	point	to	it, or	at	least	tell	whether	it	is	on	his	left	or	his	right? Can	he	make	inter-modal	comparisons among	these	presentations?	It	is	not	clear:	evidence	suggests	that	these	comparisons	emerge over	a	complex	interactive	developmental	trajectory	(Thelen,	et	al,	2001).	Either	way,	this does	not	settle	the	issue	about	shape.	Suppose	that	a	neonate	has	the	ability	to	locate	each	of a	collection	of	points	by	both	vision	and	touch.	Suppose	further	that	she	can	discriminate	by touch	whether	these	points	are	collinear	or	not.	Would	she	be	able	to	determine	by	vision whether	these	points	are	collinear	or	not?	And,	similarly,	the	newly	sighted	person?	There	is no	a	priori	reason	to	think	that	the	answer	to	these	questions	is	'yes'	and	no	reason	to	think that it is 'no'	either.	The	ability to locate	points in	space is	not the	same	as the	ability to determine whether they stand in complex spatial relations. The senses may share a representational framework for space	without sharing a representational framework for shapes. Given these observations, we propose to break the question of inter-modal comparability	of	general	ideas	of	shapes	up	into	parts	as	follows. 1. Spatial Foundation. Does the ability to locate points by touch have the same representational	basis	as	the	ability	to	locate	points	by	sight? 2. Integration Step. Given a set of points that have been located by the Spatial Foundation	of	touch	and	also	that	of	vision,	is	the	ability	to	determine	by	touch	whether	they constitute	an instance	of	a	shape	S	structurally	similar to the	ability to	determine	this	by vision? And if so, would this help, or even enable, a newly sighted person to recognize instances	of	S	by	vision	alone? Our	general	view	is	that	these	questions	have	to	be	tackled	piecemeal.	The	ability	to	locate points	may	be	context	dependent;	the	formation	of	general	ideas	of	shape	S	might	employ the	same	integrative	tools	in	two	modalities,	but	this	might	not	be	the	case	for	shape	S'. Even if Evans is right that the Spatial Foundation question should be answered positively,	this	does	not	address	the	question	of	the	Integration	Step.	And	as	we	argued	in the	preceding	section, it is	plausible to think that	different	modalities	might	address this WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 14 differently.	In	Matthen	and	Cohen	(forthcoming),	we	taxonomized	the	Integration	Step	by the	dimensionality	of	shapes.	This	allowed	us	to	bring	a	number	of	different	empirical	studies to	bear	on	the	issue,	because,	though	they	are	not	initially	addressed	to	Molyneux's	Question, they	could	be	interpreted	as	addressing	the	Integration	Step. In all of the cases we reviewed, we found that touch and vision follow different strategies	in	the	Integration	Step.	So,	in	these	cases,	the	answer	was	indeed	No.	But	we	did not	arrive	at	this	conclusion	by	a	general	argument;	we	had	to	adduce	cases	to	prove	each No.	Thus,	there	is	no	path	to	a	general	answer	to	Molyneux's	Question.	Now,	as	we'll	argue in	the	next	two	sections,	there	are	cases	where	the	Integration	Step	is	structurally	similar across modalities. Since the integrative strategies followed by different mechanisms for perceptual feature	extraction	are	diverse, there is	no reason to expect a	uniform	answer across	all	features.12 VI. Beyond Shape: The Perceptual Representation of Faces, Biological	Motion, and More So far,	we	have largely followed	mainstream	philosophical tradition in construing Molyneux's	question	as, in the first instance,	directed	at the	perceptual representation	of shape. But	our	articulation	of	the	question	into	foundational	and	integration	components invites analogous questions about the foundational and integrative roots of non-shape properties	as	well.	For	any	property	that	can	be	apprehended	by	multiple	modalities,	we	can ask:	What	are	the	foundational	elements	and	integrative	procedures	enlisted	by	the	different modalities?	And	are	these	sufficiently	similar	between	the	modalities	to	allow	crossmodal transfer	(immediately,	with	certainty,	etc.)	for	ideas	of	these	properties? This way of thinking of MQ is more fine-grained than our earlier dimensional taxonomy	in	that	it	allows	for	obstacles	to	crossmodal	transfer	between	pairs	of	modalities even	within	a	single	spatiotemporal	dimensional	regime,	and	even	when	there	can	be	other 12 Note that our pluralism about Molyneux's Question arises from our concern about particular perceptual strategies for the recovery of individual features;	Glenney (2013) and	Hopkins (2005) endorse pluralism	about	MQ	as	well,	but	for	different	reasons. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 15 cases	of	successful	crossmodal	transfer	between	those	same	two	modalities	and	within	the same	spatiotemporal	dimensional	regime. To	see	some	of	the	potential	obstacles,	and	with	the	caveat	that,	as	we've	learned	from the	shape	MQs,	we	can't	expect	our	answers	to	such	questions	to	generalize	automatically between	cases,	we	want	to	review	a	number	of	instances	where	the	evidence	suggests	that the foundational	and integration	steps	may	be	modally specific,	hence	where	crossmodal transfer	may	fail. As	an	initial	example	of	this	type,	we	can	consider	the	integrative	processes	at	work in	the	visual	representation	of	human	faces.13	Though	there	are	a	number	of	ways	to	bring out	the	special	features	of	these	processes,	one	of	the	most	striking	comes	from	the	so-called Thatcher effect-the finding (Thompson 1980) that local anomalies in the geometric organization	of	faces	are	dramatically	harder	to	detect	in	upside-down	than	in	right-side	up faces (see figure 1). This result gives us reason for thinking that at least some of the integrative processes involved in the visual representation of faces can't be understood simply	as	those	involved	the	ordinary	visual integration	of	metrical	spatial information- orientation	matters	as	well.	Faces,	then,	are	treated	as	a	kind	of	spatial	form,	but	a	kind	for which	vision	reserves	special treatment.	(This is	yet	another	way	of	making	the	point	we made at the end of section III: perceptually informed ideas of a property need not be composed	the	same	way	as	the	property	itself.) 13	Material	in	this	and	the	next	section	overlaps	with	Cohen	(2018). WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 16 Figure	1:	The	Thatcher	Effect There are several other effects suggesting that visual integration for the representation	of	faces	is	special	relative	to	ordinary	spatial	form.	Thus,	detection	times	are significantly	faster	for	faces	than	for	upside-down	faces	or	arbitrary	assemblages	of	facial features	in	non-face	arrangements	(Purcell	and	Stewart	1988;	Farah	et.	al.	1995;	Yin,	1969). Visual face recognition is susceptible to characteristic overgeneration errors: we (mis-) recognize a face in a cloud or a	mountain far	more readily than other objects. It can be selectively impaired in congenital or acquired defects (prosopagnosia) that spare other aspects	of	visual	processing (Barton	2003).	And it is	no	surprise,	given these	and	similar findings,	that	vision	devotes	special	resources	to	face	perception,	in	the	form	of	dedicated processing (Kanwisher 2010; Sinha et. al. 2006; Sugita 2009), carried out in specialized neural	areas	(Liu,	Harris,	and	Kanwisher,	2010;	McCarthy	et.	al.	1997).	(But	see	below.) Suppose	this is	all	correct	-	that, though	human	vision is	capable	of integrating	a wide	range	of	two-dimensional	spatial	forms	from	lower	dimensional	spatial	information,	its integration	of faces enjoys certain advantages relative to that	of other (equally complex) WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 17 spatial	forms	within	this	dimensional	regime.	Should	we	expect	this	fact	about	vision	to	hold of other	modalities capable of representing spatial form? Not at all. There is no ex ante guarantee that a second modality, m, that also integrates spatial information in two dimensions,	will	also	carry	out	its	integrations	of	faces	in	the	special	ways	in	which	vision appears to do. But if not, then	we should be unsurprised to find failures of crossmodal transfer	between	vision	and	m	for	representation	of	faces	(or	other	properties	to	which	the two	modalities	are	differentially	attuned). We can test this conclusion by comparing face perception in vision against face perception	in	two	other	modalities	capable	of	representing	two-dimensional	spatial	form: ordinary	haptic	touch,	and	an	artificial	modality	for	sensory	substitution	that	presents	the outputs	of	visual	transducers	to	(normal)	audition:	the	Prosthesis	for	Substitution	of	Vision with	Audition	(PSVA)	of	Capelle	et	al,	1998. Consider first the comparison to haptic touch. One significant difference between visual	and	haptic	integrations	of	two-dimensional	form	is	that	the	two	modalities	differ	in the	lower-dimensional	foundational	information	from	which	the	integrations	are	performed: vision	works from point-colours (or point-intensities) in an external space,	while haptic touch	works	from	point-pressure	in	bodily	space	(often	accompanied	by	awareness	of	willed motion of our hands and other body parts). However, despite these foundational-step differences	in	the	lower-dimensional	data	available	to	the	two	modalities,	it	turns	out	that vision	and	haptic	touch	converge	on	the	results	of	form	integrations	in	a	wide	range	of	cases. Moreover, and perhaps yet	more surprisingly, there is evidence that haptic touch treats facehood, in particular, as special in some of the	ways that vision does. Specifically, the existence	of	a	Thatcher	effect	for	haptic	touch	that	parallels	the	Thatcher	effect	for	vision (Kilgour and Lederman 2006) provides strong evidence that haptic touch, like vision, is specially attuned to facehood, relative to equally complex two-dimensional spatial forms (Lederman,	Klatzky,	and	Kitada	2010).	And,	since	the	two	modalities	align	in	apportioning importance (i.e., computational resources) to this one property of facehood, it's not too surprising to learn that there is, indeed, bidirectional cross-modal transfer for facehood between them in priming studies (Reales and Ballesteros, 1999; Easton et al.,1997a, b; WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 18 Hadjikhani	and	Roland,	1998;	Kilgour	and	Lederman,	2002;	Casey	and	Newell,	2003,	2007; Norman	et	al.,	2004).14 Now	consider	the	perception	of	two-dimensional	form	through	PSVA.	Here,	again,	the foundational	data	from	which	the	modality	integrates	two-dimensional	form	information- consisting	of	auditory	pitches	organized	temporally,	accompanied	by	awareness	of	willed motion	of	the	head/mounted	receptor	array-is	quite	different	from	the	data	on	the	basis	of which vision performs its form integrations. Should one expect that there would be significant	differences	in	the	integrative	processing	methods	employed	by	PSVA	and	vision? Our	point is that	what	we	know	about	vision	and	haptic touch	gives	us	no firm	basis for answering	this	question	one	way	or	the	other.	In	particular,	we	cannot	assume	that	the	form integrations	corresponding	to	faces	will	be	favoured	under	PSVA	(as	they	are	in	vision	and haptic	touch)	over	those	corresponding	to	equally	complex	forms.	And	there	is	no	evidence of	a	Thatcher	effect	for	PSVA.	15 What	can	we	conclude	from	the	above	evidence?	First,	it	seems	that	there	are	certain similarities between vision and touch	with regard to the construction of face-ideas. This suggests that there	will be some cross-modal carry-over between the two	modalities. Of course, it would be far too hasty to jump to a positive response to the Molyneux-type question	whether	a	newly	sighted	man	could	recognize	the	face	of	his	lover	by	sight	alone.16 And, indeed, it would be too quick even to conclude that he could immediately make judgements	like	"That	looks	like	a	hooked	nose."	For	as	we	noted	earlier,	similarity	of	content does	not imply equal ease of application.	Nevertheless,	we can expect some cross-modal parallels	between	visual	and	haptic	face	perception	that	do	not	hold	with	respect	to	the	visual and	haptic	perception	of	spatial	form	in	general.	It	would	not	be	surprising,	for	example,	to 14 Investigators	have	taken	these	findings	to	suggest	that	vision	and	touch	processes	share	at	least some	structural	representations	of faces. It	remains	controversial	whether	such	shared	representations	are more	closely	allied	with	a	format	used	by	one	of	the	modalities	(which	would	mean	that	interaction	with	the other	modality	would	involve	a	certain	amount	of	representational	remapping),	or	whether	they	are	expressed in	a	common	and	modally	unspecific	format. 15 There are other sensory substitution systems that transform visual input to auditory output; consistent	with	our	general	approach,	we	also	should	not	assume	that	any	conclusions	about	PSVA	will	extend to	these. 16	Brian	Glenney	notes	that	face-blindess	is	a	common	deficit	among	the	newly	sighted	(Fine	et	al,	2003; Cattaneo	and	Vecchi	2011:	98-102).	Whether	this	is	related	to	Molyneux's	Question	is	unclear. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 19 find that the newly blind person would preferentially pick up on certain cues for face recognition	or	be	quicker	to	learn	it	under	haptic	presentation.	So,	while	we	would	not	have an	answer	to	Molyneux's	question	for	faces,	we	would	expect	some	positive	answers	in	the general	vicinity.17 However,	we	cannot	assume	that	any	such	correspondence	would	generalize	to	other cases.	As	noted,	there	is	a	mismatch	between	the	capacities	for	integrating	faces	in	vision (where	such	integrations	are	given	special	status	relative	to	other integrations	built from spatial foundational	data)	and	in	PSVA	(where	they	are	not).	Under	these	conditions,	one would not expect that there should be crossmodal transfer of integration for facehood between	the	two	modalities.18 Having	made	these	observations,	it	is	now	natural	to	ask	whether	and	how	widely	the special	integrative	processes	at	work	in	vision	(and	perhaps	other	modalities)	extend.	On	the evidence,	there	do	appear	to	be	other	types	of	two-dimensional	spatial	forms,	beyond	human faces,	to	which	vision	(at	least)	applies	special	integrative	processes.	Take,	for	instance,	the visual system's	ability to classify	automatically,	quickly, and	easily, certain	but	not	other, equally	complex,	patterns	of	a	few	moving	points	of	light	as	reflecting	the	motion	of	key	joints in	a	moving	organism	(Johansson	1973). 17	This	is	broadly	consonant	with	the	differences	in	learning	speed	for	different	cues	reported	by	Sinha and	colleagues	for	shapes.	See	Matthen	and	Cohen	forthcoming:	section	VI. 18	Specifically,	one	would	not	expect	to	see	crossmodal	transfer	of	integration	for	facehood	from	the modality	attuned	to	the	property	(vision)	to	the	modality	not	attuned	to	the	property	(PSVA);	this leaves	it open	that	there	might	be	transfer	in	the	other	direction. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 20 Figure	2:	Subjects	visually	distinguish	moving	patterns	that	reflect	the	motion	of	key joints	in	an	organism	from	random,	but	equally	complex,	patterns. Like visual perception of faces, visual perception of biological motion appears to involve	specialized	processing	(Lu	2010),	to	be	carried	out	in	specialized	areas	(Allison	et	al 2000;	Grossman,	et	al	2000),	and	can	be	spared in injuries that	damage	gross	motor	and other	spatial	abilities (Jordan	et.	al	2002;	Kim	et.	al	2008).	Moreover, there is	a	Thatcher effect for biological motion as well: it is significantly easier to detect local anomalies (anomalies	that	perturb	the	visual	classification	of	the	motion	as	biological)	in	displays	that are	right	side	up	than	in	displays	that	are	inverted	(Troje	and	Westhoff	2006;	Mirenzi	and Hiris	2011). And,	indeed,	there	is	evidence	that	at	least	some	of	the	criteria	we	have	appealed	to in	the	foregoing	extend	to	yet	further	properties	(especially	with	perceptual	learning). Thus, Twedt, Sheinberg, and	Gauthier	2007, and	Wong	et. al. 2010 find	evidence	of a	Thatcher effect	in	vision	for	a	range	of	non-face	object	types,	including	cars,	buildings,	bikes,	and	letter strings.	And	researchers	have	found	face-like	reduced	reaction	times	in	visual	recognition tasks and	disproportionate costs for recognizing inverted figures	by experts	with a	wide range	of	non-face	domains,	including	particular	dog	breeds	(Diamond	and	Carey,	1986),	and novel	artificial	("greeble")	figures	(Gauthier	&	Tarr,	1997).19 19 The generalizability of such face-like effects to other	properties	naturally leads to	doubts about whether	the	allegedly	face-specific	processing	and	face-specific	neural	areas	are	as	domain-dedicated	as	many have	held. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 21 Taken	together,	these	results	suggest	that	vision	can	become	specially	attuned	to- can	come	to	perform	specialized	integrations	for-a	range	of	form	properties	in	a	variety	of ways,	some	perhaps	innately	specified,	some	perhaps	not.	However	wide	this	range	turns out	to	be,	it	does	seem	that	vision	is,	in	the	ways	we	have	elaborated,	more	attuned	to	some spatial	form	properties	than	others.	Thus,	even	if	it	is	true	(and	it	may	not	be)	that	the	ideas enlisted	in	the	visual	perception	of	form	all	share	a	common	spatial	foundation,	they	may nonetheless	differ	in	the	way	they	are	integrated	from	their	foundations.	And	if	there	can	be such	differences	for	ideas	of	spatial	form	within	a	modality,	there	is	all	the	more	reason	for thinking	that	crossmodal	transfer	may	fail.	For,	again,	modalities	might	build	their	ideas	of	a spatial	form	from	distinct	foundations,	and	even	if	they	share	foundations,	they	may	carry out their compositional steps in different	ways, so that	whatever special advantages (of speed,	accuracy,	etc.)	exhibited	in	a	first	modality	may	fail	to	manifest	in	a	second. VII.	Another	Clue	to	Modality-Specific	Processing:	Evidence	from	Illusion Another strategy for uncovering modality-specific forms of integration that may impede	crossmodal transfer involves	reflecting	on	classic	perceptual illusions.	Perceptual illusions	within a	modality can	be viewed as signatures of integrative	processes at	work within that modality because they reflect how these processes can go wrong in reconstructing	the	world.	That	vision	responds	to	the	Müller	-Lyer	configuration	in	its	usual, illusory, way, tells us that the processes underlying our visual integration of twodimensional	form	lead	to	a	characteristic	type	of	misestimate-one	that	may	or	may	not	be replicated	by	integrative	processes	for	the	same	two-dimensional	form	in	other	modalities.20 Now,	investigators	have	known	for	some	time	that	the	Müller-Lyer	illusion,	and	other geometric	illusions	(e.g.,	the	Poggendorff,	the	vertical-horizontal	illusion)	have	counterparts in	haptic	perception	(Bean	1938,	Over	1966).	Commentators	have	sometimes	concluded	that such	transfer	between	modalities	will	occur	quite	generally	(e.g.,	across	many	different	pairs 20	Highlighting	failures	of	crossmodal	transfer	for	this	class	of	integrations	is	also	useful	in	bringing	out that special features of particular	modalities need not be those that possess adaptive significance. This is salutary because it takes us beyond the domain of biologically significant features such as facehood and biological	motion. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 22 of	natural	and	artefactual	modalities,	especially	after	extended	perceptual learning).21	We want	to	suggest	that	the	evidence	supports	a	more	guarded	assessment:	sometimes	transfer occurs,	sometimes	it	does	not,	and	even	where	it	does	there	may	be	interesting	differences to	note. To begin with a case of successful transfer, consider the susceptibility of haptic perception	to	the	same	errors	of	line	length	estimation	present	in	visual	perception	of	the Müller-Lyer configuration. It is striking that the	effect	not	only	occurs in	both	visual and haptic	perception,	but	that	its	visual	and	haptic	manifestations	are	analogous	in	a	number	of more	specific	respects. In	both	cases,	errors	are	larger	for	more	acute	angles	(Over	1966, Heller	et.	al.	2002)	and	decrease	with	exposure	time/perceptual	learning	(Rudel	and	Teuber 1963).	In	both	cases,	explicit	instructions	to	ignore	the	fins	in	favour	of	focusing	on	bodycentered	cues reduces	error rates	significantly (Millar	and	Al-Attar	2002).	And there is	a strong	positive	correlation	between	magnitudes	of	visual	and	haptic	misestimates	within individual	subjects	(Gentaz	et.	al.	2004).	Finally,	the	haptic	effect	seems	equally	present	in sighted, sighted but blindfolded, sighted but low-vision, and congenitally blind subjects (Heller	et.	al.	2002).	This	series	of	shared	features	is	notable,	and	encourages	the	impression that	analogous	integrative	mechanisms	may	be	at	work	across	modalities. On	the	other	hand,	we	can	see	that	this	situation	is	far	from	guaranteed	by	considering a	pair	of	papers	by	Laurent	Renier	and	colleagues	on	two	classic	cases-the	Ponzo	illusion (depicted	in	figure	3)	and	the	vertical-horizontal	illusion	(depicted	in	figure	4)-in	subjects using	a	prosthesis	for	substitution	of	vision	with	audition	(PSVA)	(Renier	et.	al.	2005;	Renier, Bruyer,	and	DeVolder	2006). 21	For	example,	such	optimism	about	transfer	emerges	from	the	reports	of	Gerard	Guarniero	(1977),	a congenitally	blind	philosophy	Ph.D.	student	who	served	as	a	subject	for	Paul	Bach	y	Rita's	celebrated	work	with Tactile-Visual Sensory Substitution (TVSS), and	who	went on to write a dissertation on space perception (Guarniero	1977b),	and	also	from	the	approving	citations	of	these	remarks	by	Bach	y	Rita	(1984)	and	Noë	and O'Regan	(2002).	Unfortunately,	it	is	somewhat	unclear	what	to	make	of	these	claims:	both	because	Guarniero's reports	are	anecdotal,	and	because	it	is	not	obvious	that	the	emerging	abilities	are	perceptual	rather	than	postperceptual,	it	is	not	obvious	that	they	show	anything	at	all	about	intermodal	transfer. WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 23 Figure	3	The	Ponzo	illusion:	Parallel	horizontal	lines	of	equal	length	appear	unequal when	displayed	over	a	pair	of	oblique	lines	that	converge	toward	the	top	of	the	display. Figure	4	The	Vertical-Horizontal	Illusion:	Subjects	systematically	over-estimate	the length	of	vertical	lines. Renier	et	al	were	able	to	induce	both	the	Ponzo	and	vertical-horizontal	illusions	(in some subjects) under PSVA, but only after a non-trivial period of training	with the new modality.	This	would	seem	to	show,	by	itself,	that	facility	with	the	(characteristically	illusionWHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 24 prone) integration of two-dimensional length information in vision does not transfer immediately	to	just	any	other	modality	capable	of	recovering	two-dimensional	form. But putting things this way understates the obstacles to intermodal transfer uncovered	by	this	work.	In	fact,	Renier	et.	al.	2005	report	that,	initially,	their	subjects	were not	susceptible	to	the	Ponzo	illusion	under	PSVA	at	all,	because	they	were	able	to	perform the line length estimation task without attending to representations of the converging oblique lines	crucial to	the	visual	version	of the illusion.	Only	by	requiring	subjects	using PSVA	to	consider	the	two	oblique	lines	of	the	stimuli	before	comparing	the	length	of	the	two horizontal	bars,	could	they	make	the	illusion	re-emerge.	But	even	under	this	condition,	the effect	remained	weak:	they	found	the	effect	in	sighted	subjects	(but	still	smaller	in	magnitude than	among	control sighted	subjects	not	using	PSVA),	but	not	at all in their "early	blind" subjects	(subjects	blind	before	their	20th	month	of	age).	And	Renier,	Bruyer,	and	DeVolder (2006)	report	a	similar	pattern	for	the	vertical-horizontal	illusion:	the	effect	was	strongest in	sighted	control	subjects	not	using	PSVA,	somewhat	weaker	in	blindfolded	sighted	subjects using	PSVA,	and	completely	absent	in	early	blind	subjects	using	PSVA. These results illustrate different obstacles to crossmodal transfer for integration, even	for	a	pair	of	modalities	capable	of	recovering	two-dimensional	form	properties.	First, perceptual	expertise	for	the	relevant	integration	type	may	be	present	in	one	modality	but not	the	other,	with	the	result	that	transfer	is	impossible	without	(possibly	quite	elaborate) training.	Second,	because	perceptual	attention	may	be	fixed	in	quite	different	ways	between the two modalities, integrations that depend on which elements of a perceptual configuration	are	attended	(or	in	what	order)	may	succeed	in	one	modality	but	not	another. Third,	and	finally,	the	results	with	both	the	Ponzo	and	the	vertical-horizontal	configurations show	that	the	possibility	or	robustness	of	a	given	integrative	strategy	may	depend	on	the subject's perceptual history with a given modality; consequently, between-modality variation	in	this	respect	may	block	crossmodal	transfer	as	well. VIII.	Perceptual	Affect:	Does	It	Carry	Over? WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 25 Finally, it is	worth	noting	yet	another	perceptual	phenomenon	that falls	under ibn Tufail's	rubric	of	learning	and	potentially	under	Molyneux's	paradigm	of	crossmodal	transfer as	well.	This is the link	between	perception	and	affect in	what	has	been	called	evaluative perception. Introspection and a large and growing body of evidence reveal that our perceptual	states	have	an	affective	dimension-certain	smells	are	disgusting,	certain	tactile experiences	pleasant,	certain	flavours	repulsive,	certain	sights	and	sounds	beautiful,	certain pains	unbearable,	certain	melodies	melancholy,	and	so	on.	An	aperçu	of	Ibn	Tufail	invites	us to	consider	the	transferability	of	such	affect:	he	says	that	his	newly-sighted	man	experiences "great	joy"	when	he	becomes	visually	acquainted	with	the	colours-his	earlier	descriptive knowledge	of	them	presumably	offered	no	such	delights.	(Goodman	19xx,	7-8) Despite significant controversy about the best theoretical account of the affective dimensions	of	perceptual	experience,	we	can	take	it	as	a	relatively	uncontroversial	starting point that these	phenomena	can	be characterized in terms	of three central	psychological features: at a	minimum, affective perceptual states are valenced; they have	motivational force;	and	they	confer	reasons	to	the	subjects	in	whom	they	occur.22 Evaluative	perception	raises	all	kinds	of	interesting	questions,	but	two	in	particular are	relevant	to	our	present	investigation.	The	first,	which	is	closer	to	ibn	Tufail's,	is	whether affect	is	a	constituent	part	of	certain	perceptions	or	a	distinct	state	that	accompanies	them. Is the perceptual experience of certain melodies itself sad or melancholy, or are these emotions mere accompaniments? Would an inexperienced listener necessarily feel the emotions	of	the	"morning	effect"	when	he	listened	to	a	sensitive	rendering	of	Raga	Vibhas?23 Is startle	part and	parcel	of	hearing sudden loud sounds,	or is it a	distinct state that	has somehow	become	associated	with	them?	Would	someone	necessarily	jump	when	she	first heard	a	clap	of	thunder	or	a	flash	of	lightning?	Must	a	newly	sighted	person	become	erotically aroused	at	her	first	sight	of	a	naked	body? 22 For	useful	overviews	of	philosophical	work	on this topic, see	Aydede	and	Fulkerson (2015)	and Bergqvist	and	Cowan	(2018). 23	Raga	Vibhas,	which is	usually	played	before	sunrise, is said to	evoke	a feeling	of the	morning in listeners.	The	reader	can	judge	for	herself	at	https://youtu.be/YAt6jW8QvJE WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 26 The second, closely related to Molyneux's, is this: Is a person who experiences something	in	one	modality	subject	to	the	same	affect	as	when	she	experiences	it	in	another? Would	a	newly	sighted	person	experience	a	shape	or	a	texture	as	visually	pleasant	if	she	had previously found it haptically pleasant (holding relevant contextual dimensions fixed)? Could	she	experience	it	as	visually	pleasant	though	haptically	without	affect,	or	as	visually pleasant	and	haptically	unpleasant? We	see	no	a	priori	reason	to	believe	that	distinct	modalities	need	(or	for	that	matter need	not) bear or connect	with the same/analogous affective	dimensions at all.	Nor is it obvious,	in	the	case	that	they	do,	that	a	history	of	experiences	of	a	given	affective	type	in	one modality	will	(or	won't)	facilitate	the	acquisition	or	deployment	of	that	affective	type	in	a different modality. How soon before a newly sighted person has visual affective startle/erotic arousal/musical	pleasure?	Would	having a	history	of repulsion in	olfaction give the newly sighted person an advantage in acquiring affective repulsion in vision (relative	to	a	newly	sighted	person	without	a	history	of	olfactory	repulsion)? As in	other	cases	considered	above, there	might	not	be	a	single	answer	across the board.	We	take	it	that	the	answers	to	these	Molyneux	Questions	about	affect	are	unobvious, and	will	depend	on	the	local,	particular,	details	of	the	psychological	mechanisms	implicated by	the	specific	modalities	at	issue. IX.	Conclusion As	we	have	seen,	Molyneux's	question,	ostensibly	about	the	crossmodal	application of	sensory	knowledge,	is	a	special	instance	of	the	broader	set	of	questions	(prompted	by	ibn Tufail) about the fungibility of the senses-that is, about how knowledge and general representations/ideas	that	are	normally	formed	in	one	way	in	one	modality	can	be	formed in	another	way	in	another	modality.	This	broader	question	about	fungibility	leads	us	to	ask about the respects in	which such ideas do and do not converge, as	well as the range of crossmodal transfers they underwrite. The variety evident in the cases we've examined shows that no general answers are forthcoming: there are instances of both crossmodal divergence and convergence; and even convergence, where it is found, is insufficient to guarantee	crossmodal	transfer.	Given	all	this	variety,	it	is	likely	that	an	adequate	response	to WHAT	WAS	MOLYNEUX'S	QUESTION	A	QUESTION	ABOUT? 27 Molyneux's	question	will	require	coming	to	grips	with	the	broader	set	of	issues	raised	by	ibn Tufail.24 24	We	are	grateful	for	comments	from	and	discussion	with	Matthew	Fulkerson,	Ayoob	Shahmoradi,	and Brian	Tracz,	and	for	suggestions	from	the	editors	of	this	volume,	all	of	which	have	much	improved	the	paper. 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