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17 December 2010

Conceivability as a Guide to Possibility

In his scholarly article entitled, Does Conceivability Entail Possibility (2002), Professor David J. Chalmers of the University of Arizona examines the argument that to conceive of something necessarily entails its possibility. Chalmers states that arguments regarding conceivability and possibility typically consist of three parts; the first is the epistemic claim---conceived statement (S); the second is the modal claim---because S is conceived of, S is necessarily possible; and the third is the metaphysical claim, consisting of an assertion about the nature the universe. For example, I can conceive of that my mind exists independent of my brain, therefore it is possible that my mind exists independent of my brain, meaning that the mind is not reducible to the brain. Similarly, I can conceive of seeing without eyes, therefore it is possible that I can see without eyes, meaning that sight is not reducible to eyes, but is something independent of the eyes. But is it? In this second example, in particular, the distinction between a metaphysical possibility and a natural possibility is clear. While it is perhaps metaphysically possible to see without eyes---in a different world with different physical laws that do not require eyes for sight---in our present world, it is not naturally or physically possible to see without eyes. In broader terms, the metaphysical possibility of S does not necessarily translate to the physical or natural possibility of S. Says Chalmers in his own example:

it seems conceivable that an object could travel faster than a billion meters per second. This hypothesis is physically and naturally impossible, because it contradicts the laws of physics and the laws of nature. This case may be metaphysically possible, however, since there might well be metaphysically possible worlds with different laws. If we invoke an intuitive conception of a metaphysically possible world as a world that God might have created, if he had so chosen: it seems that God could have created a world in which an object traveled faster than a billion meters per second. So in this case, although conceivability does not mirror natural possibility, it may well mirror metaphysical possibility. (Chalmers, para. 4)

While Chalmers leaves this particular argument open-ended, he seems to be suggesting that any physical law conceived of is metaphysically possible. The test of the degree of this possibility involves further defining the degree of conceivability. According to Chalmers, there are three sub-arguments for conceivability as entailing possibility: prima facie vs. ideal conceivability, positive vs. negative conceivability, and primary vs. secondary conceivability as entailing possibility. Prima facie conceivability occurs when S is conceivable upon first appearance, or when there are no apparent contradictions to S. For example, it is prima facie conceivable that a table is made of wood if---at first glance---nothing apparently suggests otherwise. In order for S to be ideally conceivable, however, S has to pass certain tests that support it’s conceivability. In the case of the table, for example, one would have to further examine the table and still believe it to be made of wood for it to be ideally conceivable that it is made of wood. Obviously, ideal conceivability is superior to prima facie conceivability as a guide to possibility because it requires evidential support. In either case, it is the role of conceivability to verify possibility, and the role of possibility to suggest necessity. Negative conceivability occurs when S cannot be ruled out, such as in the case of a list of suspects for a particular crime. Did Jane steal the cookie? Since Jane was in the house at the time the cookie was stolen, the statement that Jane stole the cookie cannot be ruled out, therefore it is negatively conceivable---and also negatively possible---that Jane is guilty. On the other hand, the statement that Jane stole the cookie is positively conceivable only if we can conceive of a situation in which this would be true. While negative and positive conceivability might at first appear to be two sides of the same coin, Chalmers asserts that positive conceivability is the superior guide to possibility, as the role of positive conceivability is imaginative, as opposed to reductive:

Positive notions of conceivability require that one can form some sort of positive conception of a situation in which S is the case. One can place the varieties of positive conceivability under the broad rubric of imagination: to positively conceive of a situation is to in some sense imagine a specific configuration of objects and properties. It is common to imagine situations in considerable detail, and this imagination is often accompanied by interpretation and reasoning. When one imagines a situation and reasons about it, the object of one's imagination is often revealed as a situation in which S is this case, for some S. When this is the case, we can say that the imagined situation verifies S, and that one has imagined that S. Overall, we can say that S is positively conceivable when one can imagine that S: that is, when one can imagine a situation that verifies S.

It the imagination’s ability to engage rationality, therefore, that makes positive conceivability superior to negative conceivability as a guide to possibility. In either case, it remains the role of possibility to suggest necessity. The final argument for conceivability as entailing possibility compares primary conceivability---which occurs when one can think of a situation in which S actually is the case---and secondary conceivability, in which one can conceive of the epistemic possibility of S. For example, the statement that water is H2O is primarily conceivable because water really is H2O in the natural world. One the other hand, the statement that water is XYZ in secondarily conceivable because one can conceive of a world in which this true. In this argument, it is the role of primary conceivability to identify what is, and the role of secondary conceivability to identify what could have been in this world, in addition to what could be, in another physical world apart from our own. As for the role of possibility, primary possibility asserts a natural law, whereas secondary possibility suggests the existence of alternatives that law. It is Chalmers assertion that primary conceivability is the superior guide to possibility, as the foundation of primary possibility is natural actuality. While all three of the above arguments support the notion of conceivability as entailing possibility to some degree, what Chalmers seems to suggest---and I would have to agree with him---is that it is only ideal-primary-positive conceivability that necessarily entails natural possibility. Both ideal and primary conceivability engage rationality---ideal, through the rational inspection of S; and positive, through the engagement of imagination regarding S. Meanwhile, primary conceivability completely disregards metaphysical possibility, dealing instead with concrete truths about the natural physical world. While one might conceive of any number of other worlds, with any number of variations of natural laws, such conceptions are essentially inapplicable and therefore insufficient guides to possibility in the current physical world. Not to say that metaphysical conjectures are without philosophical or religious value. On the contrary, the foundation of religion and many secular philosophies is rooted in metaphysics, in which secondary conceivability is a particularly useful guide to possibility. For example, Plato’s allegory of the cave suggests that the physical world is merely a shadow of the true nature of the universe---in which case, primary conceivability is mute---while many notions of the soul all but require one to believe in a mind apart from the brain---or a soul apart from the body---which is a statement almost solely based on negative conceivability as a guide to metaphysical possibility. In other words, while types of conceivability other than ideal-primary-positive conceivability might be insufficient as guides to ideal-primary possibility, they are nonetheless necessary in order to consider metaphysical possibilities. Said Philosopher Thomas Nagel in his scholarly article entitled, What is it like to be a Bat? (1974):

A theory that explained how the mind-brain relation was necessary would still leave [the] problem of explaining why it nevertheless appears contingent. That difficulty seems to me surmountable, in the following way. We may imagine something by representing it to ourselves either perceptually, sympathetically, or symbolically . . . To imagine something perceptually, we put ourselves in a conscious state resembling the state we would be in if we perceived it. To imagine something sympathetically, we put ourselves in a conscious state resembling the thing itself . . . Where the imagination of physical features is perceptual and the imagination of mental features is sympathetic, it appears to us that we can imagine any experience occurring without its associated brain state, and vice versa. The relation between them will appear contingent even if its necessary, because of the independence of the disparate types of imagination. (Nagel, 446. fn. 11)

In addition to notions of the mind and soul, therefore, types of conceivability other than ideal-primary-positive are useful in considering the physical laws that govern beings other than oneself, to include but not limited to other life forms. For example, does water on Mars adhere to the same rules as it does on earth, or is it possible---via negative or prima facie conceivability---that it does not? In such theoretical considerations of possibility, it is the role of conceivability to suggest possibility, and the role of possibility to inspire investigation potentially leading to primary conceivability, the conception of that which is and thus the superior method of conception as a guide to the possible.

Works Cited
Chalmers, D. J. “Does Conceivability Entail Possibility?”. Concsiousness.net. Gendler, T. and Hawthorne, J. (eds). University of Arizona. 2002. Accessed 19 December, 2010 from Nagel, T. “What is it like to be a bat?” Philosophical Review 83 (1974): 435-50.