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If I can conceive it without contradiction, is it possible? Ash’arites, Hume and Kripke

Abdulrahman Al-Bassam Fellow
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Possibility & necessityAnalyticIslamicModern EuropeanAsh'arismAl-GhazaliDavid HumeRené DescartesSaul Kripke#a-posteriori-necessity#conceivability#occasionalism#possibility
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I started reading the Ash'ari theologians to understand occasionalism, and I noticed how much weight they put on one principle: whatever involves no contradiction is possible, at least for God. Al-Ghazali uses it in the Tahāfut when he says the cotton might not burn when fire touches it. No contradiction in the idea, so it is possible; the regular link we see is God's custom, not a necessity in the fire.

Then I found Hume saying something very close in the Treatise: it is an established maxim that whatever the mind clearly conceives includes the idea of possible existence. Two very different projects, one principle.

But I also know about Kripke's water and H₂O. People could conceive of water turning out to be something else, and yet, on his view, that is not genuinely possible. If that is right, conceivability is not a reliable guide after all.

So my question is open, and I would like to hear different answers: is conceivability good evidence of possibility, and if not always, when? The cotton case matters to me: if I cannot rule out that the rock behaves differently tomorrow, what is my reservoir model doing?

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5 answers

  1. Tomasz Szewczak

    Fellow

    The standard repair is to distinguish two kinds of conceivability. Before the chemistry, "water is XYZ" was conceivable in the sense that nothing you knew ruled it out. That is epistemic possibility: for all we knew. It does not show metaphysical possibility. What would show it is conceiving a scenario in full detail that genuinely includes water and lacks H₂O, and Kripke's point is that once you describe it carefully, what you are imagining is a watery stuff that isn't water.

    So: conceivability is good evidence when the conceiving is ideal and properly described, weak evidence when it just reflects ignorance. Chalmers has built a whole framework on this distinction, largely so that his zombies can survive Kripke.

  2. Layla Sfeir

    Fellow

    For the Ash'arites it was not mainly an epistemic principle. The point of saying "whatever is free of contradiction is possible" was theological: to leave God's power limited only by contradiction, and to deny that natures bind God. That is why al-Ghazali can admit we will never in fact see cotton fail to burn and still insist it is possible.

    Hume uses the same principle to the opposite end. Comparing them is very instructive, but don't let the shared maxim make them allies.

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  3. Pieter van Dijkhuizen

    Fellow

    From the engineering side: your model never assumed necessity. It assumed regularity and was calibrated to it. Whether the regularity is a necessity in the rock, a habit of God, or just how things go, your model works identically. That is a little unsettling, and also a relief.

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  4. Omar Ragab

    Fellow

    I want to defend the old principle more than Tomasz does. The Descartes route, clear and distinct conception as a guide to possibility, is still how most of us test claims of necessity. If someone says it is necessary that the universe had a beginning, my first move is to try to conceive of one that didn't. If I can, coherently, I take that as a reason to doubt the necessity. Kripke's cases are real but rare; they involve hidden natures discovered by science. For most metaphysical claims we have nothing better than careful conceiving.

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  5. Abdulrahman Al-Bassam

    Fellow

    So, if I have it: conceivability is evidence, but defeasible, and it is defeated in cases where the nature of the thing is hidden and discovered empirically. The cotton case would then depend on whether "burning" has a hidden nature that makes it necessary. Al-Ghazali would say no; a dispositionalist would say yes. That is the real dispute, not the maxim itself. Thank you, this was very useful.