Logical possibility Totally Explained

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A logically possible proposition is one that can be asserted without implying a logical contradiction. This is to say that a proposition is logically possible if there's some coherent way for the world to be, under which the proposition would be true. Thus, "the sky is blue" (and all other actually true propositions) is logically possible: there exists some logically coherent way for the world to be such that it's true, viz., the way that the world actually is. But this "way for the world to be" need not be the way the world actually is; it need only be logically coherent. So, for example, the false proposition the sky is green is also logically possible, so long as we're able (as we indeed seem to be) to conceive of some logically coherent world in which the sky is green. Philosophers generally consider logical possibility to be the broadest sort of subjunctive possibility in modal logic. Logical possibility should be distinguished from other sorts of subjunctive possibilities. For example, it may be logically possible for the universe's physical laws to be different from what they actually are. If it is, then many things that we'd normally consider to be demonstrably impossible will still be included amongst logical possibilities: for example, that information might be transmittable at speeds faster-than-light. Many philosophers, then, have held that these scenarios are logically possible but nomologically impossible, for example, impossible under the actual laws of nature.
These propositions are also to be contrasted with logically impossible propositions, for example, propositions which couldn't possibly be true under any circumstances in any universe because they're formal contradictions. While it's logically possible for the sky to be green, it isn't logically possible for the sky to be both green and not green at the same time and in the same respect, by the logical law of noncontradiction. Some combinations of physical laws are also known to result in contradictions. For instance, if a given universe's physical laws are invariant through time, then the law of conservation of energy holds in that universe. This is a consequence of Noether's theorem, which can be proven mathematically. Thus, a universe whose physical laws don't vary with time and which doesn't exhibit conservation of energy isn't logically possible.
With this understanding of logical possibility in mind, other logical modalities may be defined in terms of it: a proposition is logically necessary if it isn't logically possible for it to be false, logically impossible if it isn't logically possible for it to be true, and logically contingent if it's logically possible for it to be true and also logically possible for it to be false.

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