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Philosophical aspects of logic and set theory; truth status of mathematical axioms; Philosophy of Mathematics; philosophical aspects of mathematics in general; relation of mathematics to philosophy; etc. Consider also posting at http://philosophy.stackexchange.com/, where philosophy-of-mathematics is one of the most popular tags.

16 votes

Taking a theorem as a definition and proving the original definition as a theorem

A Grothendieck topos can be defined either as the category of sheaves on a site, or as a category satisfying Giraud's axioms, or as an elementary topos that is bounded over $\rm Set$. I believe any o …
42 votes
Accepted

Is pure mathematics useful outside of mathematics itself?

This is not really an answer to the question as asked, but I believe it's important and relevant to your problem, and too long for a comment. I will not here express any opinion about the validity or …
16 votes

Variable-centric logical foundation of calculus

Here is another approach, which I believe I first learned from Toby Bartels. Suppose $X$ is an arbitrary differentiable manifold (think of the state space of some physical system), and define a varia …
Mike Shulman's user avatar
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8 votes

How are material set theory and structural set theory related from the point of view of cate...

I think this question has not been satisfactorily studied, but we can say something. Firstly, note that since a model of SEAR (or other structural set theory) is really a category, such models form n …
Mike Shulman's user avatar
  • 66.8k
11 votes

Why would the category of sets be intuitionistic?

There are many answers that could be given, but I think the standard "algorithmically oriented" answer is the BHK/Curry-Howard interpretation, according to which a "subset $A$ of $X$" is specified by …
Mike Shulman's user avatar
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23 votes

How should a "working mathematician" think about sets? (ZFC, category theory, urelements)

There are already some excellent answers explaining in what senses ZFC can still be a foundation for most mathematics. But it also seems appropriate to mention some ways in which ZFC is insufficient …
Mike Shulman's user avatar
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6 votes

Extensionality in HoTT versus extensionality in internal language of a category

In this context, an equality is said to be "extensional" if it depends on the behavior of the objects in question, and "intensional" if it depends only on their definition. I'm not entirely sure of t …
Mike Shulman's user avatar
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21 votes

Are proper classes objects?

(Insert standard and obvious disclaimers about opinion vs. fact.) Of course proper classes are mathematical objects. The fact that we can say things like "the proper class M is a model of set theory …
Mike Shulman's user avatar
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6 votes
Accepted

Is finitism an extreme form of constructivism?

this is not a rejection of infinitism methods, but just an attempt to find a better foundation. While, constructivism is really a rejection of certain arguments. I think that's arguable. There d …
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13 votes
Accepted

evil properties, higher category theory and well-chosen tensor products

There are a lot of questions here, but I'll try to answer them all. Should every mathematical theory take place in a ∞-category? Or is 'real' mathematics basically evil? I would say that all mat …
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28 votes
Accepted

Category of categories as a foundation of mathematics

My personal opinion is that one should consider the 2-category of categories, rather than the 1-category of categories. I think the axioms one wants for such an "ET2CC" will be something like: Firs …
Mike Shulman's user avatar
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