I wonder about the nature of modal concepts such as necessity and possibility. When I say "It is possible that this page is white" or "it is necessary that two plus two equals four" I use modal words in my speech. Where do these concepts belong to? Are they in my mind or I receive them from the objects themselves?

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It's a good idea to

It's a good idea to distinguish between epistemic uses of modal language (which have to do with our knowledge) and alethic uses (which have to do with truth independently of our knowledge). When you say, "It is possible that this page is white," you might be wearing tinted glasses and simply admitting that, for all you know, the page that looks amber to you is in fact white (i.e., it looks white to normal observers in normal conditions). That use of "possible" would be epistemic. Or, instead, you might be saying that the page, which in fact emerged a mottled gray from the unreliable paper mill, could have been white had the mill done a better job. Or you might simply infer from the fact that the page is white that it's possible that the page is white: what is true is of course also possible. Those uses of "possible" would be alethic.

Where do alethic modal concepts belong? I'd say that they belong to logic, in the sense that they are at the foundation of the concept of logical consequence. To say that some proposition A is a logical consequence of some proposition B is just to say that the conjunction (B and not-A) is not possible, i.e., the conjunction couldn't have been true in any circumstances. Equivalently, it is to say that the disjunction (not-B or A) is necessary, i.e., it must be true in all circumstances.

On one way of seeing it, these modal facts are neither in your mind nor received by you from objects in the physical world. Yes, you can understand and know modal facts. For instance, you can know that possibly the page is white based on your knowledge that the page is in fact white. But modal facts would be facts whether or not your mind, or any mind, or any physical objects existed. In this way, modal facts are like the laws of logic (which depend on them) or the laws of mathematics.

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