A Warning About Constructive Foundations
September 1, 2020

A mathematical foundation chooses what existence, negation, equality, and choice mean. Those choices shape the theorems mathematicians can state, the proofs they can accept, and the programs they can extract from formal reasoning.

Axioms Change the Mathematics You Can Build

Classical logic accepts the law of excluded middle: a proposition or its negation holds. Intuitionistic logic asks for a construction before accepting many existence claims. Choice principles select elements from families of sets. Univalent Foundations gives equivalence a foundational role in equality.

Each decision changes what counts as a proof and which transformations remain valid. It can also change the computational content that a proof assistant extracts from a theorem.

Compare Consequences, Not Schools

Foundational debates become productive when they leave labels behind and compare a concrete theorem under different axioms. The comparison can trace construction, excluded middle, choice, and the effect of univalence on equivalent structures.

Putnam’s classical arguments and constructive programs deserve the same exact reading: trace each starting rule into the mathematics it enables. The result gives researchers a working map across foundations instead of an allegiance to one vocabulary.

Make the Starting Rules Visible

Choose a familiar result and formalize it twice. The differences will reveal more than a general debate ever can. They show how logic shapes existence, how proof shapes computation, and which foundation best serves the problem at hand.

Originally posted on LinkedIn

Brian Greenforest · (2020-09-01 01:10:23 UTC)

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Everything is great about Univalent Foundations and Category Theory until you give a deep thought to things like A&~A denial, axiom of choice rejection, intuitionist logic (and its school and branding "nihilistic" consequences), and to the very constructive "foundations" as their denial of classicality. Just saying. There's a "holy war" surrounding this. There's other point of view, greatly argumented by Putnam in 1960s. Fundamentalism is a famous thing in religion, too...

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Steve Haak funny you've liked this post right after our conversation about A & ~A in regard to the introduction of conflict/antagonist in creative writing.

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