I would like to ask you if we can define "possibility" (and "impossibility", "necessity" and "contingency") in the following way: If something is true, then it is possible. On the contrary, from something being possible, it does not follow that it is true. If something is necessary, then it is true. On the contrary, from something being true, it does not follow that it is necessary. I am assuming, of course, that we can easily define the four first terms from each other (for example, if something is necessary, then it is not possible that it is not true). Isn't this a good way to define possibility, at least taking "possibility" in its ordinary more or less vague meaning?