Hypothesis: In a proposition SP, if S and P differ only as more and less known then SP is logically necessary.
The most startling result is that “Water is H2O” becomes logically necessary.
Here’s three arguments for it:
1.) While there are multiple accounts of what logical possibility is, all sides seem to agree that predicating something of itself yields a logically necessary proposition. But any evidence that two terms differ only as more and less known is evidence that the same thing is being predicated of itself. Said another way, it is logically necessary that X is what it is. But where two terms differ as more and less known this obtains.
2.) Logical possibility in ancient and medieval philosophy is a failure to see a repugnance between S and P, and so necessity seems to be seeing the impossibility of repugnance between S and P. But to know that S and P differ only as more and less known is to know that it is impossible they be repugnant to each other. We can, of course, be mistaken about whether the only difference between S and P is more and less known, but to the extent that we know this it is impossible for us to judge that the two are repugnant.
3.) If you say that this is precisely why we distinguish metaphysical necessity from logical necessity, I respond: it’s no more appropriate to describe “Water is H2O” as a logical truth than as a metaphysical one. The truth is no more a matter of logic than metaphysics as it is not discovered by either.
Here’s three against:
4.) When two things differ as more or less known, one must be less certain than the other. But what is less certain can be thought otherwise, and nothing that can be thought otherwise can be considered logically necessary.
5.) Logical necessity applies to things as known and not things as they are. But a claim like “Water is H2O” is a claim about how something necessarily is and not how it is known, therefore, etc.
6.) We cannot consider something both logically necessary and open to revision. But some more known an less known things are open to revision. Therefore not all S is P related as more and less known are logically necessary.