Your question is unfair; just because you can't prove something isn't possible doesn't mean it really isn't.
Also, as all engineers, scientists, and mathematicians are aware, nothing will ever be completely proven or disproven. Even the theory and the existence of gravitational acceleration is technically "up in the air" due to the inability of humans to prove anything, but do you question it?
I am a male, but how do I prove it? We define what it is to be male, so it is subjective, and therefore impervious to proof. We assign designations to everything to that we can communicate them with each other, and in doing so render them obsolete to anything or anyone that doesn't speak our language.
Is anything possible? I don't believe so, not in the lexical sense. It is impossible for a gas to be a solid, because, according to our definition of both, one cannot exist as the other. It is impossible for a triangle to be a rectangle. It is impossible for black to be white. It is impossible for a 1957 Chevy Pickup to be a 2009 Chevy Silverado. And so on.