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Conceivability, inconceivability and cartesian modal epistemology

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Abstract

In various arguments, Descartes relies on the principles that conceivability implies possibility and that inconceivability implies impossibility. Those principles are in tension with another Cartesian view about the source of modality, i.e. the doctrine of the free creation of eternal truths. In this paper, I develop a ‘two-modality’ interpretation of the doctrine of eternal truths which resolves the tension and I discuss how the resulting modal epistemology can still be relevant for the contemporary discussion.

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Notes

  1. See (Yablo 1993; Chalmers 2002) for two influential discussions and Vaidya (2015) for a recent survey.

  2. For example, Hume argues in this way against the infinite divisibility of extension (Hume 2000, pp. 26–27), against the necessity for any event to have a cause (Hume 2000, p. 56), against the immortality of the soul (Hume 2000, p. 153). See Lightner (1997) for a study of Hume’s use of conceivability and inconceivability arguments.

  3. This view is first stated in a series of letters to Mersenne in the spring of 1630 (15 April, CSMK p. 23, AT1 pp. 145–146; 6 May, CSMK pp. 24–25, AT1 pp. 149–150; 27 May, CSMK pp. 25–26, AT1 pp. 151–153). It also appears in the Replies (CSM2 p. 261, AT7 p. 380; CSM2 pp. 293–294, AT7 pp. 435–436), in subsequent letters to Mesland (2 May 1644, CSMK p. 235, AT4 pp. 118–119), Arnauld (29 July 1648, CSMK pp. 358–359, AT5 p. 223–224) and More (5 February 1649, CSMK pp. 363–364, AT5 pp. 272–273), and in the Conversation with Burman (CSMK p. 348, AT5 pp.165–166).

  4. See in particular the letter to Mersenne of the 27th of May 1630 (CSMK p.25, AT1 p. 152) and the Sixth Replies (CSM2 p. 294, AT7 p. 436).

  5. See Frankfurt (1977) and Plantinga (1980) for the classic statement and defence of that view. Alanen (1991) defends Frankfurt’s interpretation against some objections by Curley (1984), but does not ultimately endorse the view.

  6. Other concurrent interpretations have been proposed, some of which explicitly assert that some propositions are absolutely necessary according to Descartes (Guéroult 1968, pp. 22–39). Curley (1978, p. 593) follows Guéroult on this point. See Alanen (2008) for a recent survey.

  7. In the Second Replies, Descartes defines the relation of Real Distinction as follows: “Two substances are said to be really distinct when each of them can exist apart from the other” (CMS2 p. 114, AT7 p. 162).

  8. This argument is repeated several times under Descartes’ pen, each time with an explicit move from conceivability to possibility. See CSM2 p. 54, AT7 p. 78 ; CSM2 pp.119–120, AT7 pp. 169–170 ; CSM1 p. 213, AT8 pp. 28–29.

  9. It can happen that we conceive clearly and distinctly something without something else, by an abstraction of the mind. For example, I can focus my attention on the property having three angles, as opposed to the (necessarily co-instantiated) property having three sides. But I can only do that by an operation of the intellect which abstracts away some properties from the idea I have of the object of my conception. This operation of abstraction make this conception inadequate (an adequate conception would contain all the properties the object has). It is important that we do not use conceptions obtained by abstraction when we apply (C2P), for otherwise we can easily infer the separability of things which are in fact inseparable. See the Fourth Replies for a clarification of this point (CSM2 pp. 155–156, AT7 pp. 221–222).

  10. See also the note 55, p. 27, where Yablo distances himself from Descartes: “Some philosophers use ‘imagine’ so that imagining a thing is imaging it, that is, conjuring up an appropriate sensory presentation. I do not require a sensory-like image for imagining, and certainly not a distinct such image for distinct imaginings. (Compare Descartes on the unimaginability of chilliagons at CSM II, pp. 50, 69, 264)”. Yablo seems to imply that his disagreement with Descartes about the unimaginability of chilliagons is essentially verbal, but this is debatable. If imagining and conceiving are two distinct psychological kinds, then the terminological choice of taking “imagination” as an umbrella term for both is at best misleading.

  11. “... ex his debere concludi ea omnia quae clare et distincte concipiuntur ut substantiae diversae, sicuti concipiuntur mens et corpus, esse revera substantias realiter a se mutuo distinctas; hocque in sexta concludi” (AT7 p. 17).

  12. “Et quidem jam ad minimum scio illas, quatenus sunt purae Matheseos objectum, posse existere, quandoquidem ipsas clare et distincte percipio. Non enim dubium est quin Deus sit capax ea omnia efficiendi quae ego sic percipiendi sum capax; nihilque unquam ab illo fieri non posse judicavi, nisi propter hoc quod illud a me distincte percipi repugnaret” (AT7 p. 71).

  13. “Et primo, quoniam scio omnia quae clare et distincte intelligo, talia a Deo fieri posse qualia illa intelligo, satis est quod possim unam rem absque altera clare et distincte intelligere, ut certus sim unam ab altera esse diversam, quia potest saltem a Deo seorsim poni” (AT7 p. 78).

  14. See for example how Descartes explains the argument against atomism to Gibieuf: “Et si on me disait que nonobstant que je les puisse concevoir, je ne sais pas, pour cela, si Dieu ne les a point unies ou jointes ensemble d’un lien si étroit, qu’elles soient entièrement inséparables, et ainsi que je n’ai pas raison de le nier; je répondrais que, de quelque lien qu’il puisse les avoir jointes, je suis assuré qu’il peut aussi les déjoindre de façon qu’absolument parlant, j’ai raison de les nommer divisibles, puisqu’il m’a donné la faculté de les concevoir” (AT3 pp. 477–478).

  15. See the French versions of the arguments mentioned above: (AT9 pp. 62, 131–132;AT9-2 pp. 51–52) for the Real Distinction arguments in the Meditations and the Principles of Philosophy. See (AT9-2 p. 74) for the argument against atomism and (AT9-2 pp. 72–73) for the argument against vacuum in the Principles.

  16. The Conversation with Burman (CSMK p. 339, AT5 p. 154) is very clear on this point. See also Beyssade (1981) for a detailed analysis of this topic.

  17. According to van Inwagen, for example, “philosophers who think that they can hold such concepts or states of affairs as these [i.e. a being both concrete and necessarily existent] before their minds and determine by some sort of intellectual insight whether they are possible are fooling themselves” (Inwagen 1995, p. 12).

  18. As a matter of fact, Bealer does not classify his own account as a conceivability-based account since he believes that the vocabulary of “conceivability” is misleading and should be abandoned. For Bealer takes “conceivability”, probably too literally, to refer itself to a modal fact, namely the mere possibility of having a conception. And he complains that mere possibilities cannot count as evidence, so that a decent modal epistemology should not leave any room for conceivability as a source of modal knowledge (Bealer 2002, pp. 75–76). But, of course, merely possible conceptions do not play any evidential role in conceivability-based accounts. Actual conceptions play that role. The reason why conceivability (rather than conception) is mentioned in these accounts, is that there cannot be any genuine conception of an impossibility. So conceivability, by contraposition, entails possibility. But we do not know whether something is genuinely conceivable until we have actually conceived it. So we take Bealer’s complaint against “conceivability” to be merely verbal.

  19. A discussion of Leibniz’ critique, with relevant sources, can be found in (Couturat 1901, pp. 196, 202–203). See (LoLordo 2005) for a study of Gassendi’s critique.

  20. On this point Descartes is in agreement with contemporary conceivability theorists such as Yablo (1993) who distinguishes three statuses regarding conceivability: conceivability, inconceivability and undecidability (which gathers non-conceivability and non-inconceivability).

  21. In the letter to Princess Elizabeth of the 28th of June 1643, Descartes acknowledges that “what belongs to the union of the soul and the body is known only obscurely by the intellect alone or even by the intellect aided by the imagination, but it is known very clearly by the senses” (CSMK p. 227, AT3 pp. 691–692). In other words, the union is something we can feel or experience confusedly (albeit clearly) but not something we can conceive clearly and distinctly.

  22. This notion of topical entailment is borrowed from Edelberg (1990, pp. 506–507). Although Edelberg does not mention it, Descartes defines in the Regulae a relation of necessitation between simple natures, for example between being being shaped and being extended which exactly corresponds to what he calls “topical entailments” (CSM1 p. 45, AT10 p. 421). The examples used by Descartes make it clear that this notion of necessitation applies both to propositions and properties.

  23. This is essentially the objection urged by Princess Elizabeth of Bohemia in her correspondence with Descartes. See AT3 p. 661.

  24. See the letter to Elizabeth of the 21st of May 1643 (CSMK p. 218, AT3 p. 665).

  25. It might be objected, from a contemporary point of view, that this explanation concedes too much to Descartes’ metaphysics by relying on such controversial “facts” as the identification of matter to extension or the requirement of contact for physical causation. But introducing topical entailments in the analysis of Cartesian inconceivability does not necessarily mean that we should take Descartes’ own view of the relevant topical facts for granted. If we have a better understanding of these topical facts than he had, we can form other judgements of inconceivability, which will perhaps not be Cartesian in their letter, but will nonetheless follow the analysis of Cartesian inconceivability we have proposed.

  26. Here is how Kit Fine describes this standard notion of metaphysical necessity: “This is the sense of necessity that obtains in virtue of the identity of things (broadly conceived). Thus, in this sense it is necessary not only that anything red is red or that nothing is both red and green, but also that I am person or that 2 is a number.” (Fine 2002, p. 264).

  27. For a (somewhat sympathetic) discussion of extreme haecceitism, see (Lewis 1986, pp. 239–240).

  28. That God’s power goes beyond our comprehension and that, consequently, we should never assert any sentence of the form “God cannot do ...” are recurrent themes in Descartes. See in particular the letter to Arnauld of July 29 1648 (CSMK pp. 358–359, AT5 pp. 223–224).

  29. This idea is so confused, according to Descartes, that it is impossible to know whether it represents a positive property of bodies, i.e. heat. Insofar we take it to represent a positive quality in a body, whereas it really is a privation, this idea of cold is materially false since it represents a non-thing as a thing.

  30. For the study of this derivation, we will follow closely Descartes’ own description of his acts of conception as objectual rather than propositional attitude. As mentioned earlier, this variation is insubstantial.

  31. What an atheist can keep from Descartes’ modal epistemology will be explained in Sect. 8.

  32. Such an interpretation was first suggested by Geach (1973, p. 11) and later refined by Curley (1984).

  33. These include systems such as S6, S7 and S8. One obtains S6 and S7 by adding (9) to the axioms of S2 and S3, respectively. S8 is obtained by adding \(\Box \Diamond \Diamond p\) to the axioms of S3. It is to be noted that their model theory is highly counter-intuitive in that it requires the introduction of “non-normal” worlds, where everything is possible and nothing is necessary. For further details, see Hughes and Cresswell (1972, pp. 281–284).

  34. Although standard, the view that S5 is the logic of absolute possibility is not universally accepted. According to Salmon (1989, (1984), the modal principles (S5) and (S4) and even (B) have false instances. So, if (RP) represents adequately Descartes’ view, then Descartes is not alone in recommending a logic of absolute possibility weaker than S4. The motivations of Descartes and Salmon are however very different.

  35. This kind of ‘two-modality’ interpretation was put forward by McFetridge (1990), which we follow here and elaborate upon. In particular we thereafter consider (and reject) possible objections to the interpretation which were not discussed in McFetridge’s initial paper.

  36. This qualification constitutes the substance of our “two-modality” interpretation.

  37. Moderate rationalists (BonJour 1998; Bealer 2002), as opposed to classical rationalists such as Descartes, insist that reason is fallible, although it is still taken as the primary source of justification.

  38. See however Della Rocca (2005) for a recent attempt to minimize the importance of God in Descartes’ epistemology.

  39. To be more precise, we should write “contingent\(_{1}\)”, because, if our interpretation of the doctrine is correct, it is not the same kind of modality as the one which is tracked by conceivability and inconceivability.

  40. For a presentation of these results, see for example the first chapter of (Maudlin 1994).

  41. See Bouveresse (1983, pp. 309–310) for a discussion of this point.

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Acknowledgments

I would like to thank the anonymous referees and the members of the Eidos group in Geneva for helpful comments and criticism.

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    Pierre Saint-Germier

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Saint-Germier, P. Conceivability, inconceivability and cartesian modal epistemology. Synthese 195, 4785–4816 (2018). https://doi.org/10.1007/s11229-016-1194-x

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