- #141
Hurkyl
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If a set has infinitely many elements we cannot use the word "complete" from a quantitative point of view, because no quantity can be captured and notated by one symbol, and then can be used as a meaningful input for some mathematical system.
What does "complete from a quantitative point of view" mean?
Why not?
Anyways, one thing I've told other people who don't think cardinality appropriately captures the idea of quantity is:
Don't think of cardinality as appropriately capturing the idea of quantity.
Cardinality has a rigorous set theoretical definition, which is not "Cardinality is the size of a set."
So treat it as such. It is yet another abstract mathematical idea that mathematicians use because it happens to be useful.
The same is true about ordinality. If you don't like the idea of counting to infinity and beyond, then treat it as it really is; a useful, abstract mathematical idea.
The only reason any mathematician would think as cardinal numbers as a size or ordinal numbers as counting is because it helps the mathematician understand things. For example, for me personally, such an interpretation has given be a very good intuition about transfinite induction, allowing me to very naturally extend proofs that apply in countable cases to proofs that work in uncountable cases. (Such as the proof that every vector space has a basis)
But if you don't like to think of cardinality as size and ordinal numbers as counting numbers, then don't, because, in all technicality, cardinality is not size, and ordinal numbers are not counting numbers.