I've often been taught that if we can conceive of something then it is logically possible. But more and more has suggested to me that the two concepts are analytically distinct. For example, we can often conceive of travelling back in time, however there are numerous metaphysical arguments seeming to prove that this is logically impossible. We can also conceive of a God that is omnipotent, omniscient and omnibenevolent, yet the logical problem of evil would suggest that such a concept is also logically contradictory. I don't sympathise with all of these arguments, however it would seem to me that those arguments conclusions can be true all whilst being able to conceive of the things they aim to prove to be logically impossible.

  • Do we conceive a triangle when viewing drawings of Penrose triangles?
    – J Kusin
    Commented Jan 14 at 16:56
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    Logically impossible with respect to what kind of logic? I believe answers would be easier to give if your question narrowed its domain. I would reccomend defining the terms more carefully. What do you mean by conceivable or logically possible? Commented Jan 14 at 17:29
  • You write "there are numerous metaphysical arguments seeming to prove that this is logically impossible." There is an inference there that sounds incorrect to me. I think the common understanding is that logical impossibility entails metaphysical impossibility, but not conversely. As I recall, Bacon and Zeng "A Theory of Necessities" (2021) develops a formal theory of metaphysical necessity operators which makes sense of claims like "metaphysical necessity is the weakest notion of necessity which is strictly stronger than logical necessity." I find this illuminating, and perhaps you might too.
    – user509184
    Commented Jan 14 at 18:01
  • Technically, the answer depends on definition of "conceive", but on humanly relevant ones it is no. This is closely related to the problem of logical omniscience, which was an idealizing assumption of classical epistemology that reasoners "know" all logical consequences of their assumptions. If we were ideal reasoners we'd know whether P=NP, for example. But we do not, nor can we know if our conceptions are coherent either. See also SEP, Does conceivability entail possibility?
    – Conifold
    Commented Jan 15 at 1:27
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    @sket I'd first ask what's logically possible about penrose triangles.
    – J Kusin
    Commented Jan 17 at 17:43

2 Answers 2


Your question arises because the word conceivable has a range of meanings. It can be used as a synonym for possible (or inconceivable as a synonym for impossible) or it can be used in a looser way to mean anything that might come into one's head. For example:

The idea that Marco Ocram might write a dull novel is inconceivable is an example of a play on words in which a patently conceived idea is described as inconceivable, where inconceivable is being used to mean out of the question.

I had conceived a crazy notion about a ten headed computer eating itself is an example of conceived being used to indicate a nonsensical thought.

Given the foregoing, the answer to you question is that it depends on which sense of the word conceivable you have in mind. One sense of conceivable does equate to logically possible; other don't.


To be conceivable does not have a sharp definition. In common language, what is conceivable for one person is not necessarily conceivable for a second person. On the opposite, every statement that is not contradictory is defined as logically possible, i.e. it holds in at least one possible world.

Like you I consider these two properties to be distinct. Possibly, before one accepts a certain conception or imaginates a certain state of affairs one can ask oneself “Is the conception or the state of affairs logically possible or does it produce a contradiction?” One checks the conception for logical possibility. In case it fails the test, one dismisses the conception.

Insofar I consider the conception of an omnipotent, omniscient and omnibenevolent god to be concept one has not consequently thought out.

Aside: Why do you describe yourself as a “passionate Hume disliker”?

  • Thank you for the answer. My dislike for Hume’s philosophy (not the man himself though he did certainly have some questionable beliefs from a modern perspective) references arguments I had with my tutor-mates who were staunch Hume fanboys. In reality, I respect his intellect, but disagree with his philosophical style and positions. I won’t iterate through those in this comment as it is not relevant to this thread but I’d happily do so privately.
    – sket
    Commented Jan 15 at 16:17

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