Sketch	for	a	Theory	of	the History	of	Philosophy Uriah	Kriegel My	aims	in	this	essay	are	two.	First	(§§1-4),	I	want	to	get	clear	on	the	very	idea	of	a theory	of	the	history	of	philosophy,	the	idea	of	an	overarching	account	of	the	evolution of	philosophical	reflection	since	the	inception	of	written	philosophy.	And	secondly (§§5-8),	I	want	to	actually	sketch	such	a	global	theory	of	the	history	of	philosophy, which	I	call	the	two-streams	theory. I. On	the	Very	Idea	of	A	Theory	of	the	History	of	Philosophy 1.	History	vs.	Chronology Let	us	start	with	the	distinction	between	a	history	and	a	chronology.	A	chronology	is	an unstructured	list	of	things	that	happened	–	or	more	accurately,	a	list	structured	only temporally,	that	is,	by	earlier-than,	simultaneous-with,	and	later-than	relations. Chronologies	were	prominent,	for	instance,	in	early	Greek	historiography	of	the	6th and	5th	centuries	BCE	(think	of	Herodotus'	Histories).	Especially	when	information	is scarce,	chronologies	are	extremely	valuable.	But	the	idea	of	a	history	connotes something	that	goes	beyond	a	chronology.	A	history	is	not	just	a	list	of	events,	but	an attempt	at	understanding	longitudinal	processes	of	development	(evolution)	and break	or	turning	points	(revolutions).	Thus	history	goes	beyond	chronology	in incorporating	an	element	of	theorization	or	interpretation	–	at	bottom:	an	attempt	at sense-making.	To	do	so,	it	takes	the	(nearly)	unstructured	list	of	events	and	imposes some	structure	or	organization	on	it.	At	the	very	least,	it	supplements	the	list's temporal	structure	with	a	causal	structure. One	might	think	of	a	chronology	of	philosophy	in	a	number	of	ways.	It	could	be a	list	of	all	philosophers,	a	list	of	all	philosophical	ideas,	or	a	list	of	all	philosophical texts.	In	practice	focus	has	been	on	philosophers	as	the	standard	nodes	in 2 philosophical	chronologies.	This	makes	certain	sense:	philosophical	texts	are	only interesting	insofar	as	they	express	philosophical	ideas,	and	fragmentary	philosophical ideas	coalesce	into	substantive	philosophical	conceptions,	typically,	in	the	intellects	of individual	thinkers.	Demarcating	what	makes	a	given	thinker	a	philosopher	(or	for	that matter	what	makes	an	idea	or	text	philosophical)	is	of	course	quite	the	chestnut,	but	let us	bracket	this	question	here.	What	I	want	to	highlight	at	this	point	is	only	that	a chronology	of	philosophy	is	the	starting	point	for	any	history	of	philosophy.	It	gives	us the	material,	the	data,	for	historical	theorizing. In	current	historiography	of	(Western)	philosophy,	in	practice	this	consists	in two	types	of	research,	plus	an	outlier.	The	first	type	of	research	is	work	on	the	correct interpretation	of	an	individual	thinker:	Was	Boethius	really	a	nominalist?	What	did Leibniz	mean	with	his	cryptic	but	foundational	remark	that	the	monads	have	no windows?	What	exactly	was	Russell's	theory	of	judgment?	The	other	line	of	research concerns	the	(re)discovery	of	unknown	or	lesser-known	thinkers	and	interpretation	of their	ideas.	The	recent	flourish	of	research	into	non-canonized	thinkers,	often	female, falls	within	this	line.	Who	was	George	Stout	and	what	were	his	distinctive philosophical	accomplishments?	Who	was	Margaret	Cavendish	and	what	exactly	was her	position	on	the	mind-body	problem?	Who	was	Gersonides	and	what	was	his distinctive	contribution	to	Jewish	Averroism?	Answers	to	such	questions	constitute contributions	toward	an	accurate	chronology	of	philosophy.	In	addition,	and	this	is more	of	an	outlier	in	the	historiography	of	philosophy,	some	historians	occasionally attempt	to	synthesize	others'	interpretive	work	into	something	like	a	self-conscious chronology.	In	current	research	the	gold	standard	for	this	is	Peter	Adamson's masterful	series	of	books	on	the	"history	of	philosophy	without	any	gaps." On	the	basis	of	chronologies	devised	and	refined	through	these	types	of research,	one	may	then	go	on	to	theorize	about	the	unfolding	over	time	of	philosophical ideas.	But	what	does	"theorizing"	on	the	history	of	philosophy	consist	in? 2.	What	is	a	Theory	of	the	History	of	Philosophy? Modeling	again	on	general	historiography,	I	wish	to	distinguish	four	main	stages	of potential	theorizing	in	the	historiography	of	philosophy.	They	correspond	to	(i) singular	causation,	(ii)	processes,	(iii)	causal	laws,	and	(iv)	overall	or	"total"	theory. Given	a	complete	chronology	of	things	that	happened,	one	might	wish	in	the first	instance	to	identify	individual	causal	links	between	two	particular	events.	This	is singular	causation:	the	throwing	of	the	rock	caused	the	shuttering	of	the	window,	the 3 crash	caused	the	explosion,	and	so	on.	Identifying	individual	causal	links	is	the	first stage	of	historical	sense-making.	The	second	stage	is	the	identification	of	certain	chains of	singular-causal	links.	We	may	think	of	sequences	of	such	individual	causal	links	that exhibit	the	right	kind	of	internal	cohesion	as	processes,	leading	non-accidentally	from	a start	point	to	an	end	point.	This	is	probably	the	level	of	analysis	that	characterizes most	closely	academic	historians'	research	nowadays. A	third	and	more	ambitious	stage	of	historical	theorizing,	one	that	definitely does	not	characterize	typical	historiographic	research	these	days,	would	attempt	to identify	laws	of	history.	We	move	from	singular	causation	to	causal	laws	when	we notice	that	token	events	exemplifying	certain	event-types	tend	to	cause	token	events that	exemplify	other	event-types.	The	causal	law	links	the	event	types:	the	throwing	of rocks	of	such-and-such	weight	tends	to	cause	the	shuttering	of	windows	of	such-andsuch	density.	It	is	healthy,	of	course,	to	approach	the	history	of	humanity	with	a	certain skepticism	about	the	very	existence	of	such	laws;	but	arguably,	it	is	with	the introduction	of	such	historical	laws,	if	such	there	be,	that	history	would	earn	its	status as	a	science	(on	this,	see	Comte's	Cours).	Finally,	we	can	envisage,	even	more speculatively,	that	there	is	a	single	unified	structure	to	human	history	as	a	whole.	This is	what	I	called	"total	history."	The	best-known	example	of	this	is	probably	Hegel's dialectical	theory	of	history	in	terms	of	the	progress	of	the	human	spirit,	embodied	in the	state,	through	three	stages	of	ever	increasing	freedom:	from	the	early	Asian empires	(notably	China	and	Persia),	where	only	the	despot	was	free,	through	the Greco-Roman	world	where	only	the	ruling	elites	were	free,	to	the	German	world	(what else?),	where	everybody	is	free.	If	it	was	healthy	to	approach	with	skepticism	the notion	of	historical	law,	it	is	positively	unhealthy	not	to	approach	with	skepticism	the idea	of	an	overall	pattern	in	(or	direction	of)	history;	nonetheless	a	total	theory represents	the	holy	grail	of	historiography,	parallel	in	some	respects	to	the	unification of	quantum	mechanics	and	relativity	into	a	single	overarching	theory	of	fundamental physics. As	with	general	historiography,	research	in	the	historiography	of	philosophy	is rife	that	targets	individual	causal	links,	in	this	case	between	individual	thinkers.	When we	study	Aristotle's	influence	on	Aquinas,	or	Descartes'	on	Spinoza,	or	Carnap's	on Quine,	we	conduct	this	type	of	research.	Often	the	causal	influence	is	acknowledged	by the	later	thinker,	but	sometimes	its	extent	is	unclear	prior	to	close	analysis. Rarer	in	current	historiography	of	philosophy	is	research	into	processes	in	the history	of	philosophy.	Nonetheless,	we	target	such	processes	when	we	study	the evolution	of	broadly	Scholastic	metaphysics	from	Aquinas	in	the	13th	to	Suarez	in	the 16th	century	(see,	e.g.,	Robert	Pasnau's	Metaphysical	Themes:	1274-1671);	the 4 evolution	of	German	Idealism	from	Kant	to	Hegel	(see,	e.g.,	Terry	Pinkard's	German Philosophy	1760-1860);	or	of	analytic	philosophy	from	Frege,	Moore,	and	Russell	to Quine,	Davidson,	and	beyond	(see,	e.g.,	Scott	Soames'	The	Analytic	Tradition	in Philosophy). In	contrast,	research	focused	on	the	search	for	"laws	of	history	of	philosophy"	– whereby	lawlike	causal	patterns	governing	the	formation	of	new	philosophical	ideas recurring	across	different	segments	of	the	history	of	philosophy	–	is	essentially nonexistent	nowadays.	Ditto,	of	course,	for	an	explicitly	articulated	total	theory	of	the history	of	philosophy	(whereby	a	certain	unity	of	"sense"	is	sought,	perhaps encapsulating	a	directionality).	This	type	of	research	has	vanished	from	the historiography	of	philosophy	just	as	much	as	it	has	from	general	historiography.	It	is an	open	question	whether	this	reflects	a	metaphysical	conviction	that	history	has	no laws	and	no	unity;	a	more	epistemological	suspicion	that	even	if	there	were	such	laws or	such	unity,	we	simply	could	not,	with	the	evidence	at	our	disposal,	hope	to	pin	down with	any	accuracy	or	precision	anything	resembling	a	general	law;	or	just	the	kind	of institutional	pressure	toward	ever	increasing	specialization	that	characterizes	just	as much	astrophysics	and	neurobiology,	say. In	any	case,	it	is	worth	noting	that	although	contemporary	historiography	of philosophy	does	not	feature	research	into	recurrent	patterns	or	laws	of	history,	much less	into	a	putative	overarching	unity	or	direction	in	the	history	of	philosophy,	nor does	any	work	by	historians	of	philosophy	suggest	a	refutation	of	the	ideas	lawlike patterns	or	overarching	unity.	There	is	not	even	an	explicit	statement	denying	the fruitfulness	of	any	research	on	such	questions.	The	whole	question	is	just	completely off	the	radar	in	contemporary	historiography	of	philosophy.	In	the	absence	of	any considerations	for	or	against	the	questions	of	historical	laws	or	overarching	unity,	we may	grant	ourselves	permission,	I	propose,	to	dabble	in	disciplined	speculation	on these	matters. We	may	think	of	this	part	of	the	historiography	of	philosophy	as	needing	to make	an	initial	determination	as	to	the	relative	plausibility	of	three	positions: [Skepticism] There	are	no	historical	laws,	much	less	an	underlying	unity,	to	be found	in	the	history	of	philosophy. [Optimism] There	is	no	underlying	unity	in	the	history	of	philosophy,	but	there are	recurrent	laws	we	can	identify	and	formulate. [Exuberance] There	are	laws	governing	historical	evolution	of	philosophical	ideas, and	a	certain	underlying	unity	they	embody	or	exemplify. 5 Optimists	may	then	divide	depending	on	the	kinds	of	historical	laws	they	hypothesize, and	the	exuberant	must	come	down	on	a	particular	account	of	the	overarching	unity	in the	history	of	philosophy.	In	the	next	section,	we	take	a	look	at	what	is	to	my knowledge	the	most	recent	exuberant	account	of	the	history	of	philosophy,	developed by	Franz	Brentano	(he	of	"intentionality	as	the	mark	of	the	mental")	in	the	last	decade of	the	19th	century.	It	might	be	useful,	I	am	thinking,	to	see	how	this	sort	of	thing	might look. 3.	A	Case	Study It	is	not	part	of	Brentano's	theory	of	the	history	of	philosophy	that	it	tends	toward	an endpoint.	There	is	no	direction	of	history	here	in	the	way	Hegel	and	Marx	claimed	for human	history	in	general.	Moreover,	for	Brentano	there	is	no	linear	progression	in	the history	of	philosophy	of	the	sort	we	may	observe	in	the	history	of	the	exact	and	natural sciences.	Rather	the	history	of	philosophy	resembles	more	art	history,	where	phases	of great	creativity	generating	genuine	value	are	followed	by	successive	phases	of	decline. In	particular,	claims	Brentano,	there	are	four	phases	of	philosophical developments	that	repeat	themselves	in	every	era	of	philosophy.	The	first	phase	is	the one	that	generates	great	philosophical	value	and	carries	the	torch	of	philosophical progress.	It	is	marked	by	two	main	characteristics:	a	purely	theoretical	impulse, grounded	in	true	wonder	at	the	world,	and	a	naturalistic	method	that	adapts	itself	to its	subject	matter.	This	first	phase	is	then	followed	by	three	successive	phases	of	ever grosser	decline.	In	the	second	phase,	a	practical	mindset	substitutes	the	spirit	of theoretical	wonder,	and	in	consequence,	the	applied	methodology	becomes	looser	and more	approximative.	This	leads	inevitably,	thinks	Brentano,	to	loss	of	faith	in	the advancement	of	philosophical	understanding,	and	ultimately	ushers	in	a	third	phase, characterized	by	skepticism.	However,	because	such	skepticism	can	never	quench	our inherent	thirst	for	knowledge	and	understanding,	it	is	soon	replaced	by	a	kind	of mysterian	or	mystical	inclination	characterized	by	facile	and	unprincipled	belief formation.	In	this	fourth	phase	we	linger	until	a	new	era	of	philosophy	begins,	studded with	creative	innovations	fueled	by	purely	theoretical	interest	and	oiled	by	sound methodology. Brentano's	case	for	this	recurring	pattern	is	brief	and	consists	in	claiming	a natural	placing	of	some	prominent	figures	in	the	history	of	philosophy	in	each	phase	of each	era.	The	scheme	is	displayed	in	Table	1. 6 theoretical phase practical phase skeptical phase mysterian phase Ancient Philosophy Anaxagoras	to Aristotle Stoicism	and Epicureanism Pyrrhonian Skepticism Neoplatonism Medieval Philosophy Aquinas	(and Dominicans) Scotus	(and Franciscans) Ockham	(and nominalists) Eckhart, Cusanus,	etc. Modern Philosophy Francis	Bacon and	Descartes The Enlightenment Hume Reid,	Kant,	and the	Idealists Table	1.	Brentano's	Interpretation	of	the	History	of	Philosophy The	scheme	naturally	places	Brentano's	philosophical	heroes	–	Aristotle,	Aquinas,	and Descartes	–	in	the	first,	ascendant	phases,	and	associates	his	nemeses	Kant	and	Hegel with	mystics	such	as	Meister	Eckhart.	It	also	has	the	fortuitous	if	somewhat megalomaniac	implication	that	with	Brentano	himself	a	fourth	era	of	philosophical rejuvenation	is	about	to	start.	But	setting	aside	these	problematic	features,	Brentano's scheme,	if	accepted,	would	have	the	great	virtue	of	imposing	a	clear	organization	on the	history	of	philosophy	in	toto,	thus	making	sense	of	it.	Instead	of	a	long	list	of prominent	thinkers,	we	would	get	a	highly	structured	narrative. In	particular,	Brentano's	theory	of	the	history	of	philosophy	clearly	provides	us with	laws	of	historical	development.	We	can	think	of	such	statements	as	"a	skeptical phase	leads	to	a	mysterian	phase"	as	capturing	a	basic	kind	of	law.	In	addition, however,	we	can	see	the	statement	"each	era	is	characterized	by	the	same	progression through	four	phases"	as	a	sort	of	supreme	historical	law,	the	law	that	captures,	in	a way,	the	deep	uniformity	in	the	history	of	philosophy. One	may	quibble	of	course	with	the	specifics	of	Brentano's	theory.	Why	and how	did	Aquinas	get	to	be	the	first	Medieval	philosopher,	wondered	Étienne	Gilson, perhaps	the	greatest	medievalist	of	the	first	half	of	the	20th	century	–	do	we	not	have over	half	a	millennium	of	medieval	philosophical	reflection	before	him?	Likewise,	we may	wonder	whether	Reid	is	really	a	mysterian.	Brentano	treats	him	so	because	Reid grounds	all	knowledge	in	otherwise	ungrounded	"commonsense	beliefs."	This	seems	a bit	thin	as	a	reason	to	lump	Reid	together	with	the	likes	of	Plotinus	and	Hegel.	In	fact, the	attachment	to	common	sense	seems,	in	temperament	at	least,	all	the	opposite	of the	allure	of	mystical	flights. More	deeply,	I	find	it	more	than	a	little	suspicious	that	the	organization	of chronologies	into	cycles	featuring	the	battle	of	good	versus	evil,	with	eventual	rebirth of	the	good	to	launch	a	new	cycle	–	this	abstract	and	somewhat	cartoonish	pattern	–,	is 7 such	a	recurring	theme	in	many	traditions'	quasi-mythological	histories.	Even	the number	four	seems	to	come	up	time	and	again	in	these	systems,	for	instance	in	Hindu and	Zoroastrian	conceptions	of	history.	Might	there	not	be	something	about	our cognitive	hardwiring	that	pushes	us	to	impose	cyclical-cum-tetralogical	order	on	the phenomena,	instead	of	it	being	the	phenomena	themselves	that	recommend	these four-phase	cycles? In	addition,	one	may	also	raise	an	eyebrow	about	Brentano's	dogmatic acceptance	of	the	standard	periodization	of	the	history	of	philosophy	in	terms	of Ancient,	Medieval,	and	Modern	eras.	This	periodization	leaves	much	to	be	desired,	as we	will	now	discuss. 4.	Periodization Perhaps	the	most	elementary	way	to	impose	initial	structure	on	an	otherwise unstructured	list	of	events	is	through	periodization:	segmenting	the	list	into	more	or less	self-contained	sub-lists.	Although	in	itself	a	merely	temporal	specification,	the choice	of	periodization	reflects	a	certain	conception	of	the	causal	coherence	internal	to each	period,	with	passage	to	a	new	period	indicating	a	break	in	normal	processes	of development.	To	that	extent,	the	periodization	we	adopt	of	any	history	betrays	a commitment	to	a	bird's	eye	view	analysis	of	the	major	streaks	in	that	history. The	most	standard	periodization	of	human	history,	the	one	we	all	learned	at school,	starts	history	with	the	advent	of	historical	records	(dismissing	everything	prior to	that	as	"pre-history")	and	dividing	history	into	three	main	periods:	the	Ancient world,	going	roughly	from	the	founding	of	Rome	in	the	mid-8th	century	BCE	to	its collapse	at	the	end	of	the	5th	century	CE;	the	Middle	Ages,	spanning	roughly	500-1500; and	Modernity,	from	"the	age	of	discovery"	circa	1500	to	the	present.	Wherefrom	came to	our	schools	this	particular	periodization?	The	answer	is	not	entirely	clear.	Early Renaissance	thinkers,	notably	Petrarch	and	Leonardo	Bruni,	have	already	divided Western	history	into	three	important	segments,	in	which	the	dark	Middle	Ages interrupted	the	intellectual	and	cultural	growth	of	ideas	in	the	Ancient	Greco-Roman world,	to	be	reborn,	so	to	speak,	with	the	Renaissance.	This	periodization	was popularized	in	the	17th	century	by	the	German	historian	Christoph	Keller	(a.k.a. Cellarius).	But	the	model	became	entrenched,	and	enriched	with	the	concept	of "prehistory,"	primarily	through	the	German	Enlightenment;	the	works	of	August Ludwig	von	Schlözer	on	"universal	history"	in	the	final	third	of	the	18th	century	are representative	here. 8 As	we	know,	the	standard	periodization	of	the	history	of	(Western)	philosophy, inscribed	in	the	academic	curriculum,	is	essentially	the	same:	we	have	(1)	Ancient Philosophy,	going	from	Thales	in	the	7th	century	BCE	to	circa	500;	(2)	Medieval Philosophy,	going	basically	from	500	to	1600;	and	(3)	Modern	Philosophy,	starting with	Descartes	in	the	early	17th	century	and	still	ongoing.	Each	of	these	mega-periods also	admits	of	a	more	or	less	standard	sub-periodization	in	the	curriculum.	Thus	we divide	Ancient	Philosophy	into	(1.1)	the	Pre-Socratics	(7th	–	5th	BCE),	(1.2)	Socrates, Plato,	and	Aristotle,	(1.3)	Hellenistic	philosophy	(4th	BCE	–	3rd	CE),	and	(1.4)	Late Antiquity	(3rd	–	6th	CE);	Medieval	Philosophy	into	(2.1)	the	Early	Middle	Ages	(6th	– 10th	CE),	(2.2)	the	High	Middle	Ages	(11th	–	13th),	and,	sometimes	but	not	always	set apart,	(2.3)	Renaissance	Philosophy	(14th	–	16th);	while	Modern	Philosophy	we	divide into	(3.1)	Early	Modern	(17th	-18th,	Descartes	to	Kant),	(3.2)	19th-century	philosophy, and	(3.3)	20th	century	to	the	present	(starting	with	Frege,	Moore,	and	Russell	for analytic	philosophy,	Husserl	for	phenomenology). A	curious	feature	of	this	standard	periodization	is	that	it	is	entirely	derivative from	the	periodization	of	human	history	in	general	–	it	takes	into	account	exactly nothing	specific	to	the	development	of	philosophical	ideas.	This	is	in	truth	very	odd.	Is there	really	a	reason	we	should	expect	philosophical	turning	points	to	align	so perfectly	with	turning	points	in	the	history	of	humanity	more	generally?	Perhaps	there is	such	a	reason,	say,	as	far	as	political	philosophy	is	concerned.	But	when	it	comes	to metaphysics,	say,	it	would	be	very	surprising	if	the	rise	and	fall	of	Rome	should coincide	with	the	rise	and	fall	of	abstracta,	or	if	the	"age	of	discovery"	that	ushered	in Modernity	happened	to	coincide	with	the	rise	of	idealism.	At	any	rate,	even	if	major events	in	human	history	did	trigger	important	philosophical	developments,	why should	the	absence	of	major	historical	events	encourage	the	absence	of	important philosophical	developments?	We	might,	on	the	contrary,	expect	long-term	stability	to provide	the	foundations	for	contemplative	progress;	or	we	might	expect	individual genius	to	show	up	in	complete	independence	of	historical	context. As	soon	as	we	take	critical	distance	from	this	standard	periodization	of	the history	of	philosophy,	its	flaws	become	instantly	evident.	I	will	name	only	two. Arguably,	the	most	important,	most	decisive	century	in	the	whole	of	(Western) philosophy	is	that	from	Plato's	birth	to	Aristotle's	death.	Whitehead	famously	said	that the	philosophical	tradition	consists	in	a	series	of	footnotes	to	Plato.	As	I	will	later suggest,	Whitehead	was	half	right	and	very	wrong:	it	would	be	more	accurate	to	say that	half	the	philosophical	tradition	consists	in	footnotes	to	(i.e.,	elaborations	of)	Plato; the	other	half	consists	in	footnotes	to/elaborations	of	Aristotle.	Yet	this	pivotal	subperiod	occurs	in	the	middle	of	the	standard	period	we	call	Ancient	Philosophy.	In	a 9 proper	periodization,	I	suggest,	that	fateful	century	would	launch	a	new	stage	in	the history	of	philosophy.	This	is	an	instance	where	a	crucial	juncture	in	the	history	of philosophy	corresponds	to	no	pivotal	event	in	the	larger	history	of	human	affairs. Secondly	(and	conversely),	when	we	look	for	a	major	philosophical	turning point	to	accompany	the	fall	of	Rome	in	476,	and	to	signal	a	transition	from	the	first	to the	second	great	supposed	periods	of	Western	philosophy,	we	come	up	blank.	The	best candidate	is	surely	Boethius'	Consolation	of	Philosophy,	as	well	as	his	earlier commentaries	on	Aristotle	and	Porphyry.	But	although	Boethius	was	very	influential	in the	Middle	Ages,	he	is	generally	regarded	as	a	relatively	derivative	thinker,	mostly combining	and	modifying	familiar	Aristotelian,	Neoplatonist,	and	Christian	ideas.	And it	is	noteworthy	that	most	philosophy	graduates	today	earn	their	B.A.	without	ever hearing	of	Boethius	in	the	classroom	–	or	indeed	outside	it.	Clearly,	then,	we	do	not	in fact	designate	Boethius	as	a	crucial	figure	marking	a	turning	point	in	the	history	of philosophy. To	be	clear,	I	am	personally	a	big	fan	of	Boethius,	whom	I	take	to	have	a	strong claim	to	being	the	first	(Western)	nominalist.	But	my	point	is	once	removed	from	the first-order	question	of	the	merit	in	Boethius'	philosophical	ideas.	The	question	I	am raising	is	rather	this:	since	we	do	not	in	fact	take	Boethius	to	represent	anything	like the	kind	of	turning	point	in	the	history	of	philosophy	that	we	take	the	fall	of	the	Roman Empire	to	be	in	Western	history,	why	do	we	align	the	periodization	of	the	history philosophy	with	that	of	the	history	of	human	affairs	writ	large?	This	alignment	seems in	truth	entirely	artificial. Why,	then,	do	we	cut	up	the	history	of	philosophy	the	way	we	do?	One	line	of thought	is	that	any	periodization	of	the	history	of	philosophy	is	bound	to	be	arbitrary to	some	extent,	so	we	might	as	well	adopt	an	otherwise	familiar	framework	for	cutting it	up.	Now,	in	this	form,	the	claim	seems	to	me	a	tad	too	strong	–	surely	some	putative periodizations	are	better	than	others.	Nonetheless,	it	is	quite	likely	that	a	multiplicity of	possible	periodizations	would	prove	equally	good,	at	least	from	certain	perspectives, and	anyway	there	are	probably	no	"facts	of	the	matter"	about	the	correct	periodization. However,	this	point	by	itself	does	not	quite	justify	uncritical	acceptance	of	the	standard periodization	of	the	history	of	philosophy.	In	fact,	it	encourages	the	floating	of alternative	periodizations	and	their	comparison	with	the	standard	one	and	with	one another. II. The	Parallel-Streams	Theory 10 5.	Two	Philosophical	Temperaments In	the	remainder	of	this	paper	I	want	to	sketch	the	kind	of	theory	of	the	history	of philosophy	that	I	find	most	initially	appealing.	Indeed	I	take	this	to	be	the	most	banal and	undaring	theory	of	the	history	of	philosophy	one	might	come	up	with.	Its	main virtue	is	just	in	being	a	theory	–	a	theory	of	the	history	of	philosophy	as	a	whole. I	will	start	by	sketching	a	portrait	of	two	opposing	philosophical	temperaments. I	will	call	them	Temperament	A	and	Temperament	B	to	avoid	any	baggage	that	might come	with	more	illuminating	labels,	though	one	would	not	be	too	far	off	the	mark	if instead	one	called	them	the	Platonist	and	Aristotelian	temperaments.	I	will	then	sketch a	way	to	model	the	development	of	philosophical	ideas	in	terms	of	the	interaction	of three	forces	feeding	into	individual	thinkers'	work,	resulting	in	the	parallel development	toward	the	self-articulation,	if	you	will,	of	a	stable,	maximally	plausible	Atype	worldview	and	a	stable,	maximally	plausible	B-type	worldview. My	portrait	of	the	two	temperaments,	in	Table	2,	is	in	the	style	of	caricature.	I imagine	that	a	single	philosopher	embodies	all	A-type	temperamental	characteristics and	another	embodies	all	B-type	characteristics.	In	practice,	the	vast	majority	of philosophers	are	thankfully	more	complex	intellectual	personalities.	But	caricature	has its	expository	virtues. Temperament	A Temperament	B in metaphysics, a	welcoming	attitude	toward	all manners	of	abstracta	and universals,	seen	not	just	as necessary	concessions	but	as agreeable	liberators	from	the dreariness	of	concrete	reality; a	marked	preference	for nominalism	and	desert	landscapes, not	just	as	outputs	of	fair-minded evaluation	of	arguments	but	as	a precondition	for	a	serious	attempt to	make	sense	of	the	world; in	(the	part	of metaphysics we	now	call) philosophy	of mind, an	anti-materialist	instinct	that spans	the	gamut	of	dualism, idealism,	and	other	ways	of recognizing	something	other than	brute	matter	among	the ungrounded	grounds	of	reality; a	strong	attachment	to materialism	(or	"	physicalism"	in the	newfangled	jargon); in epistemology, a	tendency	toward	rationalism and	intuitionism,	with	a	faith	in	a an	empiricist	inclination	to	base	all knowledge	on	observational 11 Table	2.	Caricature	of	Two	Basic	Philosophical	Temperaments A	very	similar	opposition	is	proposed,	incidentally,	by	William	James	in	Chap.	1	of Pragmatism.	James	distinguishes	between	"two	kinds	of	philosopher,"	one	of	whom	he calls	tender-minded	and	characterizes	as	"Rationalistic	(going by	'principles'), Intellectualistic,	Idealistic,	Optimistic,	Religious,	Free-Willist,	Monistic,	Dogmatical"; the	other	he	calls	tough-minded	and	characterizes	as	"Empiricist	(going	by	'facts'), Sensationalistic,	Materialistic,	Pessimistic,	Irreligious,	Pluralistic,	Sceptical."	I	bracket for	present	purposes	the	question	of	whether	James'	is	in	fact	the	same	distinction,	but with	differences	of	emphasis	due	to	different	philosophical	climate,	or	a	similar	but priori	principles	as	epistemic foundations	from	which	the	rest of	our	knowledge	is	deductively inferred; encounter	with	particular	facts	– dated	and	localized	occurrences	– and	inductive	rather	than deductive	inference	from	them; in	moral philosophy, a	rationalist	approach	that	seeks to	derive	commonly	accepted moral	precepts	from	a	priori moral	principles; a	more	sentimentalist	attempt	to ground	moral	understanding	in concrete	emotional	experience rather	than	pure	reason; in philosophical methodology, a	willingness	to	accept	mysterian and	sometimes	even	mystical elements	in	a	complete	picture	of the	world	(footnote:	for	religious philosophers,	enter	credo	quia absurdum	etc.); a	naturalism	that	puts	a	premium on	explanations	that	appeal	only	to posits	internal	to	the spatiotemporal	realm	(footnote: for	religious	philosophers, substitute	rational	theism); in	metaphilosophical sensibility, a	tireless	monism	convinced	that the	plurality	in	appearance	must belie	an	ultimate	unity	in noumenal	reality,	and	indeed that	reality	only	becomes	fully intelligible	when	this	unity	is uncovered; a	skeptical	attitude	toward	the monistic	drive	and	a	greater	trust in	pluralistic	accounts	that	resist forcing	unity	on	the	phenomena; in philosophical prose, an	emphasis	on	the	literary	and Humanistic	qualities	of presentation	and	an acknowledgement	of	the	role	of rhetoric	in	communicating	ideas. a	dry	and	literal	style	that	prizes clarity	and	precision	above	all	and takes	as	its	model	science	writing rather	than	literature. 12 slightly	different	distinction.	I	just	mean	to	signal	a	certain	precedent	to	the	distinction I	draw	between	Temperaments	A	and	B. As	noted,	it	is	natural	to	see	Plato	and	Aristotle	as	prototypes	of	type-A	and type-B	philosophers.	(Here	I	use	"prototype"	in	the	industrial	sense	of	the	term,	so	to speak;	in	the	sense	in	which	it	is	used	in	the	cognitive	psychology	of	concepts,	to	mean something	like	paradigm,	the	honors	may	go	rather	to	Plotinus	and	Hume.)	Plato's well-known	metaphysics	of	a-spatial	and	a-temporal	Forms	as	what	is	most	real,	his idealism	and	arguments	for	the	incorporeality	and	immortality	of	the	soul,	as	well	as his	account	of	knowledge	as	innate	and	only	recalled	(rather	than	acquired)	with	the aid	of	sense	perception	–	all	present	already	in	the	Phaedo	–	testify	to	his	A temperament;	and	of	course	Plato's	dialogues	afford	some	of	the	greatest	literary delights	of	all	philosophical	prose.	Meanwhile,	Aristotle's	focus	on	the	metaphysics	of material	objects	and	his	understanding	of	in	re	universals	as	enclosed	within spacetime,	his	integrated	hylomorphist	account	of	the	mind-body	relationship,	his straightforward	empiricist	statement,	in	De	Anima	III,	that	"if	we	did	not	perceive anything,	we	would	not	learn	or	understand	anything,"	and	his	appreciation	for	the variety	and	multiplicity	of	phenomena,	perhaps	most	evident	in	his	biological	works, all	stand	in	testimony	to	his	B	temperament;	but	no	reader	of	the	Metaphysics	would accuse	its	author	of	excess	lyricism,	however	awestruck	we	might	be	by	his	sheer brainpower. 6.	Two	Parallel	Streams It	is	useful	for	my	proposed	theory	of	the	history	of	philosophy	that	Plato	and	Aristotle fit	the	A	and	B	molds	so	well,	because	for	almost	two	millennia	following	them,	the history	of	philosophy	was	almost	self-consciously	the	result	of	the	ongoing	competitive juxtaposition	of	a	Platonist	and	an	Aristotelian	worldview,	modulo	the	occasional dismissal	of	both	as	relics	of	dangerous	paganism	or	their	attempted	synthesis	into	a single	worldview	of	"the	philosopher."	All	the	way	up	to	the	Renaissance	we	find philosophers	time	and	again	designating	themselves	as	Platonist	or	Aristotelian,	or dedicating	themselves	to	commentary	or	analysis	of	Platonic	and/or	Aristotelian	texts. From	my	perspective,	though,	it	is	not	Plato	and	Aristotle	themselves	that	define	the subsequent	unfolding	of	the	history	of	philosophy.	Rather,	they	play	the	special	roles they	do	only	because	they	happen	to	offer	early	and	near-perfect	embodiments	of Temperaments	A	and	B. Insofar	as	two	thousand	years	of	(Western)	philosophy	self-consciously	lend themselves	to	modeling	in	terms	of	a	competitive	juxtaposition	of	early	embodiments 13 of	Temperament	A	and	Temperament	B,	a	model	of	the	entire	history	of	philosophy	as organized	around	the	parallel	development	and	self-articulation	of	these	two philosophical	temperaments	carries	initial	plausibility.	It	is	mostly	the	extension	of	the model	into	Modern	Philosophy	that	requires	an	element	of	"creativity"	on	the	theory's part.	But	in	truth	the	commonplace	division	of	Modern	philosophers	into	rationalists and	empiricists	maps	relatively	neatly	onto	Temperaments	A	and	B	as	well	(hence James'	division	of	philosophers	into	Rationalist	lovers	of	principles	and	Empiricist lovers	of	facts).	My	own	view	is	that	the	standard	classification	of	Descartes	as	a rationalist	is	something	of	a	historiographical	blunder,	but	bracketing	the	case	of Descartes,	it	is	not	hard	to	appreciate	how	Spinoza,	Kant,	and	19th-century	German and	British	Idealists	partake	in	Temperament	A,	or	how	Temperament	B	is	exemplified by	the	British	Empiricists,	19th-century	continental	positivists	like	Auguste	Comte	and Ernst	Mach,	as	well	as	Brentano	and	some	of	his	followers,	notably	the	"Polish	logicians and	nominalists,"	as	Ernest	Nagel	called	them	in	what	is	probably	the	first	selfconscious	use	of	the	expression	"analytic	philosophy"	–	Nagel's	1936	paper "Impressions	and	Appraisals	of	Analytic	Philosophy	in	Europe." With	these	remarks	in	place,	let	me	now	provide	a	sketch	of	two	parallel streams	in	the	history	of	philosophy,	an	Aand	a	B-stream.	I	issue	a	series	of	caveats immediately	thereafter. • Plato • Speusippus,	Xenocrates,	and	the Old	Academy • Philo	of	Alexandria,	Plutarch,	and the	other	Middle	Platonists • Seneca,	Epictetus,	and	most	Stoics • Plotinus • Porphyry,	Augustine,	Boethius, and	other	Neoplatonists • Anselm,	Bonaventure • Marsilio	Ficino,	Cusanus,	and other	Renaissance	Humanists • Descartes,	Spinoza,	Leibniz • Cudworth	and	the	Cambridge Platonists • Aristotle • Peripatetics	from	Theophrastus through	Alexander	of Aphrodisias	to	Andronicus • Epicureans	from	Epicurus	to Lucretius • Boethius • Al-Farabi,	Averroes,	Maimonides, and	later	Averroists • Aquinas,	Ockham,	and	most	late Scholastics • Suárez,	Francis	Bacon • Descartes • From	Locke	through	Hume	to Mill:	three	centuries	of	British 14 • Kant • Fichte,	Schelling,	Hegel	and	other German	as	well	as	British	Idealists • G.	E.	Moore,	neo-Kantians Empiricism • Comte	and	Mach	(early positivism) • Brentano	and	most	parts	of	the Brentano	School • The	Vienna	Circle	and	Quine Now	to	the	caveats.	First,	note	that	the	two	streams	are	not	exclusive.	I	have included	Boethius	and	Descartes	in	both,	because	each	seems	to	me	to	have	initiated philosophical	developments	of	the	first	significance	within	both	streams.	(I	bracket here	my	reasons	for	saying	this;	the	point	is	just	that	there	is	nothing	inherently problematic	in	the	notion	of	such	dual	contribution.)	Secondly,	my	two	streams	are not	exhaustive	either:	I	am	not	sure,	for	instance,	where	if	anywhere	to	place American	Pragmatism,	Husserl,	or	Wittgenstein.	(The	problem	may	be	just epistemic,	insofar	as	more	sustained	analysis	would	issue	in	some	recommendation; but	there	may	also	be	no	fact	of	the	matter	about	such	things.)	Thirdly,	it	is important	to	keep	in	mind,	in	any	case,	that	most	philosophers	fit	neither	caricature very	closely,	and	I	am	assigning	them	to	one	stream	rather	than	another	mostly because	they	resemble	one	caricature	more	than	they	do	the	other.	Fourthly, obviously	the	choice	of	who	to	include	on	these	lists	reflects	a	certain	view	about who	the	important	figures	are	in	each	era.	Here	I	have	not	exercised	any	personal judgment	but	have	simply	placed	canonical	figures	on	the	list.	But	a	proper development	of	a	theory	of	the	history	of	philosophy	should	exercise	judgment. Finally,	and	most	importantly,	it	is	perfectly	possible	to	disagree	about	the	proper classification	of	some	of	these	thinkers.	I	can	see	the	case,	for	instance,	for	denying Boethius	a	place	in	the	B-stream,	or	according	Al-Farabi	a	subsidiary	assignment	in the	A-stream.	However,	to	quarrel	about	the	proper	assignment	of	this	or	that	figure in	stream	A	or	B	is	not	itself	to	question	the	usefulness	of	organizing	the	history	of philosophy	along	these	two	streams.	As	a	tool	for	imposing	structure	on	what	is otherwise	a	brute	chronology	of	philosophy,	the	division	of	the	history	of philosophy	into	developments	in	Temperament	A's	self-articulation	and Temperament	B's	self-articulation	may	prove	illuminating	–	that	is,	it	may	help	us see	real	order	and	real	patterns	in	the	history	of	philosophy	–	even	if	it	is	not	always immediately	clear	where	an	individual	philosopher	is	best	placed	within	this superstructure. Is	there	a	direction	to	the	history	of	philosophy,	if	this	is	how	we	think	of	it? There	certainly	need	not	be,	and	perhaps	owing	to	my	own	B-ish	temperament,	I	am disinclined	to	think	of	history,	philosophical	or	otherwise,	in	teleological	terms.	(I am	with	Ranke	and	Herzen	against	Hegel	and	Marx	on	this!)	Nonetheless,	it	is 15 certainly	possible	to	imagine	two	natural	"resting	points"	for	the	history	of philosophy	as	modeled	here.	The	first	is	the	convergence	on	something	resembling long-term	consensus	on	what	the	stablest	and	most	ultima	facie	plausible philosophical	package	deals	are	tailored	to	A-type	antecedent	sensibilities	and	Btype	sensibilities.	The	second	is	the	fashioning	of	the	stablest	and	most	ultima	facie plausible	synthesis	of	the	two	outlooks. As	duly	promised,	the	above	is	almost	banal	as	a	theory	of	the	history	of philosophy.	Much	of	it	is	generated	by	stitching	together	two	dividing	lines	familiar from	standard	historiography	of	philosophy	–	the	Platonist/Aristotelian	line	for Ancient	and	Medieval	philosophy	and	the	rationalist/empiricist	line	for	Modern philosophy	–	to	reconstruct	two	more	or	less	continuous	streams	of	unfolding philosophical	developments.	The	distinctive	claim	here	is	mostly	just	that	the underlying	rationale	for	this	organization	has	to	do	with	a	dichotomy	between	two opposing	philosophical	temperaments,	namely,	those	caricatured	above. 7.	Mechanics	of	Progression Given	an	organization	of	the	history	of	philosophy	along	two	parallel	streams,	how are	we	to	understand	the	evolution	of	ideas	within	each	stream?	My	suggestion	is that	an	individual	thinker's	philosophical	ideas	are	the	resultants	of	three	forces. The	first	is	the	influence	of	earlier	thinkers	of	similar	temperament.	The	second	is counter-influence,	so	to	speak,	by	challenges	the	thinker	perceives	as	emerging	from the	opposing	philosophical	temperament.	The	third	is	the	thinker's	own	intellectual impetus,	imparting	on	his	or	her	work	the	distinctive	and	unpredictable	quality	that makes	the	history	of	philosophy	such	a	"live"	process. Different	thinkers	will	exhibit	different	admixtures	of	these	three	forces	in their	philosophical	"output."	On	the	whole,	we	seem	to	designate	as	key	figures	in the	history	of	philosophy	those	we	take	to	(i)	have	a	larger	than	usual	portion	of personal	impetus	in	the	formation	of	their	ideas	and	(ii)	exercise	a	larger	than	usual influence	and/or	counter-influence	on	subsequent	thinkers.	Philosophers	we	take	to exhibit	(i)	but	not	(ii),	or	(ii)	but	not	(i),	tend	to	sit	on	the	cusp	of	our	pantheon	– they	are	objects	of	intense	scholarship	but	do	not	typically	show	up	in	the undergraduate	curriculum	(Brentano	may	fit	the	first	profile,	Averroes	the	second). Among	the	philosophers	we	take	to	exhibit	both	(i)	and	(ii)	–	that	is,	highimpetus	philosophers	exercising	considerable	influence	and	counter-influence	– certain	further	distinctions	may	be	made.	In	particular,	we	might	distinguish	three 16 profiles:	(a)	those	thinkers	who	are	themselves	susceptible	primarily	to	counterinfluence	(e.g.,	Kant,	slumber-woken	as	he	is	by	Hume),	(b)	those	more	susceptible to	straightforward	influence	(e.g.,	Aquinas,	drawing	primarily	on	Aristotle),	and	(c) those	appearing	to	form	their	philosophical	ideas	almost	entirely	from	internal impetus	(Descartes?).	Here,	too,	of	course,	caricatures	are	useful	in	bringing	out more	sharply	what	in	reality	are	much	blurrier	affairs. Within	the	framework	I	am	proposing,	a	history	of	(Western)	philosophy would	trace	the	development	of	ideas	as	a	function	of	the	forces	of	influence, counter-influence,	and	impetus	swirling	in	each	stream,	the	A	stream	originating	in Plato	and	the	B	stream	originating	in	Aristotle.	Those	streams	develop	at	some periods	in	relative	isolation	from	each	other,	at	others	through	intense	crossfertilization	or	even	partial	merging,	but	most	of	the	time	somewhere	in-between.	It is	very	unusual,	though,	for	developments	in	one	stream	to	be	comprehensible without	any	reference	to	preceding	and	roughly	contemporaneous	developments	in the	other.	Full	appreciation	of	the	one	is	thus	likely	to	require	substantial appreciation	of	the	other.	Still,	we	may	legitimately	view	each	stream	as	seeking primarily	its	most	plausible	self-articulation	given	the	challenges	posed	by	the	other stream. What	kind	of	historical	laws,	if	any,	should	we	expect	in	a	parallel-stream model	of	the	history	of	philosophy?	We	might	hope	to	find,	at	a	suitable	level	of descriptive	abstraction,	certain	recurring	patterns	in	the	way	individual philosophers	build	on	predecessors	to	develop	ever	purer	embodiments	of	one philosophical	temperament;	here	the	mini-histories	of	Late	Scholasticism,	British Empiricism,	and	German	Idealism	might	provide	fertile	material.	On	the	other	hand, we	might	also	hope	to	discover	recurring	patterns	in	the	way	individual philosophers	develop	breakthrough	ideas	in	reaction	to	challenges	they	perceive from	thinkers	of	the	opposing	philosophical	temperament.	Here	we	might	think paradigmatically	of	Aristotle's	reaction	to	Plato,	Kant's	reaction	to	Hume,	and	the two	roughly	simultaneous	and	broadly	"analytic"	reactions	to	19th-century idealism:	Moore	and	Russell's	to	British	Idealism	and	Brentano's	to	German Idealism.	If	certain	abstract	regularities	can	be	found	across	these	cases,	they	might serve	as	prima	facie	hypotheses	about	historical	laws.	These	would	be	putative	laws of	influence	and	putative	laws	of	counter-influence.	I	personally	suspect	there	are	not also	"laws	of	impetus"	for	us	to	seek:	individuals'	idiosyncratic	intellectual	impetus is	precisely	what	injects	into	the	history	of	philosophy	its	contingent,	accidental, unpredictable	(in	a	word:	Dionysian)	dimension. 17 In	addition	to	such	laws	of	influence	and	counter-influence,	we	also	have	the "supreme	law"	that	the	history	of	philosophy	progresses	in	two	parallel	streams,	in which	the	stablest	and	most	ultima	facie	plausible	philosophical	package	deals	are sought	that	would	articulate	Temperament	A's	and	Temperament	B's	antecedent sensibilities.	This	is	our	counterpart	to	Brentano's	law	that	each	era	in	the	history	of philosophy	is	characterized	by	the	same	progression	through	four	phases.	It	is	what captures	the	most	fundamental	structure	we	are	trying	to	impose	on	the	chronology of	philosophy. 8.	Periodization	Again I	want	to	close	with	some	remarks	on	how	periodization	of	the	history	of	philosophy should	be	approached	within	the	parallel-streams	framework.	But	perhaps	the	most important	upshot	of	the	framework	is	that	we	approach	the	history	of	philosophy wrongly	when	we	slice	it	"horizontally,"	along	historical	periods,	and	expect	periodbased	academic	specialization.	We	do	the	history	of	philosophy	greater	justice,	in fact,	when	we	slice	it	"vertically,"	along	longitudinal	segments	of	the	two	parallel streams	I	have	sketched,	and	encourage	specialization	in	the	evolution	of	ideas across	time	within	either	stream.	This	kind	of	historian	of	philosophy	does	exist:	for the	A-stream,	we	have	the	work	of	Raymond	Klibansky,	who	published	on	Plato, Proclus	and	other	Neoplatonists,	the	reception	of	Platonic	ideas	in	Byzantine	and Islamic	philosophy,	and	the	continuity	through	the	Middle	Ages	all	the	way	to Cusanus	in	the	Renaissance	(see,	e.g.,	Klibansky	1939);	for	the	B-stream,	see	notably the	work	of	Hamid	Taieb,	who	has	published	on	B-type	thinkers	from	Aristotle	and Alexander	of	Aphrodisias	though	Aquinas	and	Peter	Auriol	to	Brentano	and Twardowski,	inter	alia	(see,	e.g.,	Taieb	2018).	But	the	academic	norm	is	clearly horizontal	rather	than	vertical	specialization.	This	makes	a	certain	amount	of professional	sense.	Vertical	scholarship	obviously	requires	non-trivial	linguistic	and historical	competencies.	Still,	as	noted	it	seems	to	me	to	do	greater	justice	to	the internal	logic	of	the	history	of	philosophy,	and	is	more	likely	to	bring	us	nearer	a correct	understanding	of	the	overall	history	of	philosophy. That	said,	it	is	an	independently	interesting	question	how	we	should approach	the	periodization	of	the	history	of	philosophy	within	the	parallel-streams framework.	Here	two	(entirely	compatible)	periodization	projects	suggest themselves	to	me. The	first	project	is	to	segment	each	stream	separately	into	its	own	distinctive periods.	What	are	the	turning	points	in	Temperament	A's	philosophical	self18 articulation,	and	what	in	Temperament	B's?	For	A,	we	might	for	instance	designate Plato	to	Plotinus	as	the	first	era,	Plotinus	to	Kant	as	the	second	era,	and	post-Kantian A-type	philosophy	as	the	era	we	are	still	in;	and	for	B,	we	might	take	Aristotle	to Aquinas	as	the	first	era,	Aquinas	to	Bacon	as	the	second	era,	the	half-millennium	of predominantly	Anglophone	empiricism	and	positivism	between	Bacon	and	Quine	as a	third	era,	and	post-Quinean	B-type	philosophy	as	a	fourth	era	now	in	its	infancy (see	Table	3).	I	am	proposing	this	periodization	mostly	for	the	sake	of	illustration. But	there	are	several	general	points	it	serves	to	illustrate.	First	of	all,	the philosophical	periodization	need	not	align	with	the	Schlözer-style	periodization	of Western	history	into	Ancient,	Medieval,	and	Modern.	Secondly,	the	periodizations	of the	A	stream	and	B	stream	need	not	align	with	each	other;	in	fact,	there	is	little reason	to	expect	them	to.	Thirdly,	periods	can	vary	greatly	in	their	length	–	there	is no	reason	to	expect	neat	roughly	millennium-long	periods	in	the	history	of philosophy.	And	fourthly,	we	may	find	that	one	stream	naturally	segments	more fine-grainedly	than	the	other;	again,	there	is	no	a	priori	reason	to	expect	anything else. • Plato • Plotinus • Kant • Aristotle • Aquinas • Bacon • Quine Table	3.	A	Possible	Two-Stream	Periodization	of	the	History	of	Philosophy A	second	periodization	project	within	the	parallel-streams	framework	would seek	to	segment	the	overall	history	of	(Western)	philosophy	by	the	relative	longterm	dominance	of	Temperament	A	or	Temperament	B	in	the	philosophical landscape.	Three	types	of	possible	periods	might	be	distinguished:	when Temperament	A	is	dominant,	when	Temperament	B	is	dominant,	and	when	neither dominates.	Thus,	we	might	designate	the	period	between	Plato	and	Plotinus	as	a first	era	of	no-dominance;	the	period	between	Plotinus	and	Averroes/Aquinas	as	a second	era,	dominated	by	Temperament	A;	the	period	from	Aquinas	to	Spinoza	as 19 dominated	by	the	B	temperament;	and	thereafter	a	fourth	period	of	renewed	nodominance. • Plato/Aristotle • Plotinus • Aquinas • Spinoza No	dominance A-dominance B-dominance No	dominance Table	4.	A	Possible	Single	Periodization I	close	with	four	general	notes	on	these	two	periodization	projects.	First, both	projects	invite	sub-periodizations	as	well.	Thus,	even	if	the	current,	fourth stage	in	our	single	overall	periodization	is	characterized	by	no-dominance,	it	might seem	natural	to	view	the	half	century	from	Descartes	to	Locke	as	A-accented,	the following	century	–	from	Locke	to	Kant	–	as	B-accented,	and	the	following	century	as A-accented	again.	It	is	just	with	a	coarser-grained	look	that	we	see	the	larger	period as	more	balanced. Second,	if	we	start	our	two	historical	streams	with	Plato	and	Aristotle,	we	are effectively	confining	Socrates	and	his	predecessors	to	the	pre-history	of	philosophy, somewhat	as	Schlözer	sent	pre-Roman	humanity	into	the	Dunkle	of	pre-history.	This seems	to	me	in	truth	quite	justified,	if	only	because	we	have	essentially	no	written material	from	these	thinkers,	only	quotations	and	testimonies	by	others	(much	of what	we	know	about	the	pre-Socratics	comes	originally	from	Aristotle	and Theophrastus,	and	almost	everything	we	know	about	Socrates'	philosophy	comes from	Plato). Third,	as	noted	I	do	not	expect	there	to	be	theory-independent	facts	of	the matter	that	rationally	compel	us	to	accept	one	possible	periodization	over	all	others. The	idea	of	'natural	joints'	in	the	history	of	philosophy,	which	it	is	the	historian's aim	to	correctly	identify,	has	little	purchase	on	us	as	we	survey	the	mass	of philosophical	works	that	constitute	the	history	of	philosophy.	This	raises	difficult 20 methodological	questions	around	the	evaluation	of	proposed	periodizations,	and raises	the	specter	of	possible	cohabitation	of	several	of	periodizations	co-accepted in	parallel.	I	bracket	these	questions	here,	since	anyway	I	am	floating	the periodizations	in	Tables	3	and	4	mostly	for	illustrative	purposes. Fourth,	there	will	be	a	temptation	for	contemporary	philosophers	to	ask	how certain	living	philosophical	giants	–	say,	Saul	Kripke	or	Kit	Fine	–	might	fit	into	the various	schemes	I	have	put	forward	here.	Such	questions	are	fun	to	play	with,	but	in truth	I	think	we	should	resist	the	temptation	to	speculate	on	the	historical significance	of	the	Kripkes	and	Fines	of	the	world,	as	we	simply	lack	the	distance	to evaluate	their	influence	and	counter-influence	on	the	evolution	of	philosophical ideas	on	the	timescales	relevant	to	a	history	of	philosophy.	This	point	extends	to recently	deceased	giants	(say,	David	Lewis)	as	well.	Although	this	is	often	not	the case	today,	traditionally	academics	in	history	department	have	worked	with	a moving	wall	of	half	a	century	to	a	century	when	it	comes	to	defining	what	is	history. This	perfectly	reasonable	rule	of	thumb	would	recommend	silence	for	now	on	the historical	place	of	the	likes	of	Lewis,	Kripke,	and	Fine. 8.	Conclusion,	with	Coda	on	Non-Western	Philosophy In	a	way,	my	main	aim	in	this	paper	has	been	to	invite	a	more	critical	approach	to the	branch	of	philosophy	we	call	history	of	philosophy:	more	critical	both	regarding its	official	aims	and	regarding	some	of	its	deepest,	most	institutionalized assumptions,	notably	around	periodization.	I	have	floated	an	expanded	agenda	for the	historiography	of	philosophy	that	includes	more	global	concerns	with	the overall	structure	of	the	history	of	philosophy,	and	have	also	recommended	a	more philosophically	based	approaches	to	the	periodization	of	the	history	of	philosophy. In	a	more	speculative	vein,	I	have	also	sketched	first-order	proposals regarding	both	the	overall	structure	of	the	history	of	philosophy	(i.e.,	in	terms	of	the parallel	developments	of	two	opposing	philosophical	temperaments'	search	for their	best	articulation)	and	fruitful	periodizations	in	light	of	that	basic	structure	(i.e., the	ones	captured	in	Tables	3	and	4). In	various	places,	I	have	indicated	parenthetically	that	my	subject	matter	is restricted	to	"Western"	philosophy,	which	designation	typically	covers	European civilization	and	its	Modern	extension	in	the	Americas.	But	in	truth	geography	has little	to	do	with	our	subject	matter.	Any	thinker	whose	work	has	the	same	aim	as what	we	call	philosophy,	and	who	exemplifies	to	an	extent	Temperament	A	or	B, 21 would	belong	to	the	history	of	philosophy	as	conceived	here.	This	applies	obviously to	such	figures	as	Iamblicus	the	Syrian	Neoplatonist,	Avicenna	the	Persian Aristotelian,	and	Amo	the	African	Cartesian.	But	it	may	perfectly	well	apply	to thinkers	who	did	not	engage	the	philosophical	tradition	of	the	West	at	all,	so	long	as these	thinkers'	intellectual	concerns	and	aims	overlap	sufficiently	with	those	of	the figures	mentioned	above,	especially	if	their	pursuit	of	these	aims	manifests	elements of	Temperament	A	and/or	B.	From	this	perspective,	there	is	absolutely	no	reason not	to	include,	say,	the	6th/7th-century	Indian	philosopher	Dharmakīrti	in	our	Bstream,	given	his	apparent	nominalism	and	empiricism. It	is	an	open	question,	of	course,	just	what	the	proprietary	aim	of	philosophy exactly	is.	Different	people	will	have	different	views	on	this	(see	my	"Philosophy	as Total	Axiomatics"	for	my	own	views).	But	whatever	one's	view,	it	should	make	it possible	for	a	historical	figure	entirely	insulated	from	the	European	philosophical tradition	to	show	up	in	the	same	history	of	philosophy.	Such	a	figure	would	not,	of course,	participate	in	the	same	causal	web	of	influence	and	counter-influence. Dharmakīrti's	nominalism	was	not	influenced	by	Boethius'	and	did	not	influence Ockham's.	But	they	may	yet	participate	in	a	separate	web	(Dharmakīrti	is	a	highly influential	figure	in	Indian	philosophy,	and	was	himself	strongly	influenced	by Dignāga),	and	anyway	sufficiently	bizarre	circumstances	could	lead	some	European thinker,	too,	to	be	causally	insulated	in	this	way.	From	this	perspective	there	is	no reason	why	non-Western	thinkers	could	not	be	placed	within	a	single	global	history of	philosophy. At	the	same	time,	presumably	some	intellectual	pursuits,	including	ones	no less	valuable	than	philosophy,	would	not	qualify	as	philosophical	on	any	minimally substantive	characterization	of	philosophy's	distinctive	intellectual	aims.	And	some of	these	pursuits	could	be	labeled	"philosophy"	despite	their	dissimilarity	to	the pursuit	shared	by	the	thinkers	we	have	mentioned	here.	In	that	case,	all	sides	may be	generous	in	allowing	everybody	to	use	the	label,	but	it	would	be	useful	to	keep	in mind	the	fact	that	different	things	are	being	talked	about.	Almost	half	a	century	ago now,	Kwasi	Wiredu	argued	that	much	of	what	is	discussed	under	the	banner	of African	Philosophy	is	in	fact	not	philosophy	at	all:	often	the	gambit	is	to	draw	out broadly	philosophical	or	cosmological	propositions	implicit	in	collective	myths	and oral	traditions	specific	to	African	ethnicities,	whereas	philosophical	reflection	is characterized	precisely	by	the	rigorous	and	analytic	making	explicit	of	ideas	of	some universal	import.	Of	course	Wiredu	allows	for	the	possibility	of	African	philosophy in	the	sense	pertinent	to	us	here,	but	for	him	it	is	simply	good	old-fashioned philosophy	that	happens	to	be	done	by	Africans.	Compare:	when	we	speak	of European	architecture	versus	Asian	architecture,	we	have	in	mind	a	significant 22 distinction	between	two	kinds	of	architecture;	but	when	we	speak	of	European tomatoes	and	Asian	tomatoes,	we	assume	that	tomatoes	are	tomatoes	are	tomatoes and	we	are	simply	keeping	track,	for	whatever	reason,	of	where	some	of	them	come from.	The	history	of	"Western"	philosophy	is	more	like	a	history	of	Western tomatoes	than	a	history	of	Western	architecture. The	point	–	the	point	I	am	adopting	here	from	Wiredu,	that	is	–	is	that,	at bottom,	philosophy	is	one	–	even	if	it	is	interesting,	for	whatever	reason,	to	keep track	of	where	in	the	world	that	one	thing	is	done.	Again,	we	do	not	object	to	the polysemous	use	of	"philosophy"	to	designate	other	intellectual	pursuits.	We	only insist	that,	in	the	sense	in	which	the	term	"philosophy"	is	used	here,	there	is	no meaningful	distinction	between	the	history	of	Western	philosophy	and	histories	of non-Western	philosophies.	Since	philosophy	is	one,	the	history	of	philosophy	is	also one.1 Works	Referenced § Adamson,	P.	2014.	Classical	Philosophy.	Oxford:	Oxford	University	Press. § Adamson,	P.	2015.	Philosophy	in	the	Hellenistic	and	Roman	Worlds.	Oxford:	Oxford University	Press. § Adamson,	P.	2016.	Philosophy	in	the	Islamic	World.	Oxford:	Oxford	University	Press. § Adamson,	P.	2019.	Medieval	Philosophy.	Oxford:	Oxford	University	Press. § Aristotle.	De	Anima.	Google	it. § Aristotle.	Metaphysics.	Google	it. § Boethius	524.	The	Consolation	of	Philosophy.	Trans.	P.G.	Walsh.	Oxford:	Oxford University	Press,	1999. § Brentano,	F.	1895.	'The	Four	Phases	of	Philosophy	and	Its	Current	State.'	Trans.	B.M. Mezei	and	B.	Smith.	In	their	The	Four	Phases	of	Philosophy.	Amsterdam:	Rodopi,	1998. § Comte,	A.	1830-42.	Cours	de	philosophie	positive.	Paris:	Rouen. § Gilson,	E.	1939.	'Franz	Brentano's	Interpretation	of	Mediaeval	Philosophy.'	Mediaeval Studies	1:	1-10. § Hegel,	G.W.F.	1837.	Lectures	on	the	Philosophy	of	History.	Trans.	J.	Sibree.	London:	G.	Bell and	Sons,	1902. 1	For	comments	on	a	previous	draft,	I	am	grateful	to	Peter	Adamson	and	Maurice	Kriegel. 23 § James,	W.	1907.	Pragmatism:	A	New	Name	for	Some	Old	Ways	of	Thinking.	New	York: Longmans,	Green,	&	Co. § Klibansky,	R.	1939.	The	Continuity	of	the	Platonic	Tradition	During	the	Middle	Ages. London:	The	Warburg	Institute. § Kriegel,	U.	2016.	'Philosophy	as	Total	Axiomatics:	Serious	Metaphysics,	Scrutability Bases,	and	Aesthetic	Evaluation.'	Journal	of	the	American	Philosophical	Association	2: 272-290. § Marx,	K.	and	F.	Engels	1846.	The	German	Ideology.	Trans.	W.	Lough,	C.	Dutt,	and	C.P. Magill.	New	York:	International	Publishers,	1970. § Nagel,	E.	1936.	'Impressions	and	Appraisals	of	Analytic	Philosophy	in	Europe.'	Journal	of Philosophy	33:	5-24. § Pasnau,	R.	2011.	Metaphysical	Themes:	1274-1671.	Oxford:	Oxford	University	Press. § Pinkard,	T.	2002.	German	Philosophy	1760-1860:	The	Legacy	of	Idealism.	Cambridge: Cambridge	University	Press. § Plato.	Phaedo.	Google	it. § von	Schlözer,	A.L.	1772.	Vorstellung	seiner	Universal-Historie. Göttinger:	Dieterich. § Soames,	S.	2014.	The	Analytic	Tradition	in	Philosophy,	Vol.	1:	The	Founding	Giants. Princeton:	Princeton	University	Press. § Soames,	S.	2017.	The	Analytic	Tradition	in	Philosophy,	Vol.	2:	A	New	Vision.	Princeton: Princeton	University	Press. § Taieb,	H.	2018.	Relational	Intentionality:	Brentano	and	the	Aristotelian	Tradition.	Cham: Springer.