That word most readily brings to mind the parallel postulate, which is independent from Euclid’s other four.
If that is completely unhelpful to you, then to me it is something that is taken without proof. In other words, one does not need to do geometry (or set theory, depending on which we are talking about) with the thing. One can take some other postulate instead. (edit: or none at all)
What I meant in my other post is that the infinity axiom is an axiom (postulate), and hence is not proved.
Pug:
Mea culpa. I did not read it that way, sorry. Yes, you are extremely close. A “postulate” is an
assumption granted for the sole purpose of allowing an argument to proceed. But, it never stops being an
assumption. An axiom is more akin to a “law” of physics. That’s the problem. Mathematicians run around the halls of academia spouting off all sorts of gibberish until, at some point, they begin to believe that mathematics takes on more
objective reality than is possible for it. The undergirding for mathematics is
physical objects. But,
mathematical objects are objects of a different sort, as St. Thomas says:
“
In the framework of immateriality, the mathematician in his strictly scientific character is said to
leave aside all sensible matter and to retain in the abstracted result universal intelligible matter.” -
Summa Theologica, I, q. 85, a. 1, reply 2
I’m sure not too many mathematicians would like this either.
The
infinity axiom is a postulation. In real arithmetic, a person can point to
5 cows. A person can point to
1,000 head of cattle. And, a person can
imagine a billion head of cattle. But, such an imaginary object is grounded in its ostensible possibility in
reality. The problem with
infinity, is that it is
not a number. It is a contraction (to borrow from Rossum) that
“objectifies” it so that it may be talked about and possibly manipulated in some manner. But, the term itself represents something nebulous. It represents a vagary. There is no number that is represented by the word. In fact, the word means “
unbounded.” It is a contraction of the concept an unimaginably huge number. And, it has been known for centuries that it is that which is by definition,
dynamic.
It can grow; it can be reduced. This is precisely what makes it vague. However, at any stopping point - where its dynamicality is halted, such as
closing it within a system - it becomes
finite. The formulation of the axiom must, therefore,
deny finite sets within the equation. Why is this so hard to ratiocinate? I theorize that it is caused by nothing more than loosing sight of
the fact of reality. As an imaginary object, it is real enough. But, it does not survive outside of the mathematician’s mind, imagination. The
infinity axiom does not have the basis, i.e, existentiality, of, say, the Law of Gravity. Furthermore, the infinity axiom depends upon other axioms (postulations) that do not carry as much weight as the axiom itself
seemingly carries. But, I am always amazed at how people think.
“The mathematician, scientific in Aristotle’s sense, makes two abstractions: one, to go from the sensible world to the order of individual intelligible matter; the other, to go to the universal or common consideration of intelligible matter itself.”
This is the two-step process by which the human mathematician reifies his material so that it can be
worked with. But, that doesn’t mean that his
material is worked with in the same way as a carpenter works with wood.
God bless,
jd