Their ontology has nothing to do with their truth.
Of course it does. A proposition which does not exist, cannot have a truth value associated with it.
If all concepts are merely “products of the mind,” how is the truth of those concepts determined? Is it arbitrarily assigned by the mind? Based upon what, exactly? Correspondence to reality, perhaps? No? If not, then what is the point of playing the mind game?
Truth and falsity are also concepts. They do not exist apart from a mind. A proposition can refer to a state of affairs in (physical) reality, and we assign a truth value to it, if it correctly represents reality. Or the proposition refers to an abstract system, and then we assign a truth value to it, if it is a logical corollary of the axioms.
I intended to put “proof” in scare quotes because, you are correct, inductive methods do not result in proofs, strictly speaking.
Ok, that is agreeable.
Arbitrarily chosen? Not exactly.
Not all axiomatic systems are equally useful. The axioms and postulates of Euclides proved to be very useful, and yet, they were generalized by Riemann and Gauss-Bolyai-Lobatchevsky and all of a sudden, two brand new “worlds” were born. The usually accepted axiomatic set of mathematics “grew out” of the desire to describe reality as accurately as possible. As such they are not “arbitrary”, since reality is not arbitrary. But one can create other axiomatic systems, for other purposes. Like… read on… chess!
Chess is another axiomatically defined system, the size of the board, the pieces, the rules are the axioms. None of those are “necessary”, there are all sorts of modifications. But in championship chess, the axioms MUST be adhered to.
I arbitrarily specified it. It’s one of those axioms one assumes by definition. In this case the container is part of the axiomatic system that the null set depends upon in order to have any meaning at all.
You can try it, and no one will pay attention, just like if you started to “redefine” the rules governing the movements of the pieces in chess. You might come up with some interesing axiom-set, and you might get a following. But those axioms are still arbirtary.
What defines the null set, then, if not a container? If nothing defines the null set, it doesn’t exist apart from any other set.
I am not going to waste months on teaching you set theory. Go and take a few courses at your nearby college.
Sounds like you are playing a mental game.
Welcome to the real world. Mathematics is a “mind game”, pretty useful, too, since it reflects the physical reality (of course it is superfluous to add “physical”, since there is no other reality). Philosophy is also a “mind game”, much inferior. But it can be amusing.