Hume on Conceivability and Inconceivability

Hume Studies Volume XXIII, Number 1, April 1997, pp. 113-132 Hume on Conceivability and Inconceivability D. TYCERIUM LIGHTNER What other simple Ideas 'tis possible the Creatures in other parts of the Universe may have, by the Assistance of Senses and Faculties more or perfecter, than we have, or different from ours, 'tis not for us to determine. But to say, or think there are no such, because we conceive nothing of them, is no better an argument, than if a blind Man should be positive in it, that there was no such thing as Sight and Colours, because he had no manner of Idea, of any such thing, nor could by any means frame to himself any Notions about Seeing. John Locke, An Essay concerning Human Understanding, IV iii 23J At several important places in the Treatise2 and the first Enquiry,3 Hume speaks of some things as being conceivable, other things as being inconceivable, and relates these claims to a thing's being possible or impossible, respectively. These places include his discussion of abstract ideas, his argument against the necessity of the principle of induction, his argument against the claim that everything must have a cause, and his argument that space and time are not infinitely divisible. Several times, Hume clearly infers the possibility of something from its conceivability. What is not so clear, however, is whether he ever infers the impossibility of something from its inconceivability. John P. Wright, in his rich work The Sceptical Realism of David Hume, argues that Hume ultimately rejects the universal principle that whatever is inconceivable is impossible, even though, Wright states, Hume D. Tycerium Lightner is at the Department of Philosophy, The Ohio State University, Columbus OH 43210-1365 USA. homepage: http://www.geocities.com/Athens/3067 email: tycerium@geocities.com 114 D. Tycerium Lightner employs the principle early in the Treatise.4 Thus Wright's interpretation seems to render Hume's position inconsistent, or at least has Hume reversing himself in the course of the Treatise. It would be desirable to find an interpretation of Hume's texts that avoids this. It is also unclear exactly what Hume means by "can" when he states that something "can be conceiv'd." It might mean that something can be conceived given our actual mental abilities and our actual pool of simple ideas with which we construct complex ideas. Or, it might mean that it can be conceived in some more idealized situation, such as one where we have a complete pool of simple ideas to draw upon, perfect memory, and a perfect ability to separate and combine ideas. In order to have a clear understanding of Hume's notion of conceivability, and the arguments that involve this notion, we must determine both the force of the modality in this notion and whether Hume thought that inconceivability implies impossibility. We shall find that when Hume speaks of conceivability he means what can be conceived given our actual abilities and actual pool of simple ideas. Also, we shall find that Hume rejects the claim that whatever is inconceivable is impossible. This rejected generalization, however, must be distinguished from the narrower principle that if forming an idea of something would involve forming a contradictory idea, then that thing is impossible. Hume accepts this latter principle.5 1. Conceivable and Possible, Inconceivable and Impossible Hume held that the ability to conceive something clearly and distinctly implies its possibility. This principle, which we shall call the Conceivability Principle, is stated by Hume in many passages and in many different forms. Here are some of them: nothing of which we can form a clear and distinct idea is absurd and impossible. (T 19-20) 'Tis an establish'd maxim in metaphysics, That whatever the mind clearly conceives includes the idea of possible existence, or in other words, that nothing we imagine is absolutely impossible. (T 32) Whatever can be conceiv'd by a clear and distinct idea necessarily implies the possibility of existence... (T 43) ...whatever we conceive is possible, at least in a metaphysical sense... (A 65O)6 The contrary of every matter of fact is still possible; because it can never imply a contradiction, and is...