## New Directions in the Philosophy of Mathematics October 8, 2008

Posted by dcorfield in Uncategorized.

To celebrate the founding of MIMS, the mathematics department of the recently unified Manchester University, it was proposed that various workshops named ‘New Directions in…’ be run. They kindly agreed to allow Alexandre Borovik and me to organise one of these workshops on the Philosophy of Mathematics.

So, on Saturday 4 October, we began with Mary Leng, a philosopher at Liverpool, talking about whether the creation of mathematical theories, e.g., Hamilton’s quaternions, gives us any more reason to think mathematical entities exist than does the discovery of new consequences within existing theories. She concluded that it does not — both concern the drawing of consequences from suppositions, e.g., “Were there to be a 3 or 4-dimensional number system sharing specified properties with the complex numbers, then…”.

George Joseph, author of The Crest of the Peacock, then told us about sophisticated work in 16th century Kerala concerning expansions of trigonometric functions, and better proved equivalents to the proto-calculus of Wallis. He then moved on to China where in search of the equally tempered scale, the 16th century Chinese mathematician Zhu calculated the value of $2^{1/12}$ to an extraordinary number of decimal places. Discussion centred around the question of why we continue to ignore non-Western roots of modern mathematics.

Marcus Giaquinto, a philosopher from University College London, talked about visual intuition and proof. He explained how a great deal of care is needed in assuring ourselves of the validity of a geometric demonstration. This follows up on the work of Ken Manders (Pittsburgh) to understand when Euclidean diagrammatic reasoning is valid.

Angus MacIntyre, a model theorist at Queen Mary College London, told us about the limited interest for mainstream mathematics of incompleteness results. He argued that the kind of Diophantine equations appearing in incompleteness results are not of the kind number theorists deal with, and he explained to us how he is trying to show that Wiles’ proof of Fermat’s Last Theorem can be written in first-order Peano arithmetic.

I finished off the talks by speaking about my paper Lautman and the Reality of Mathematics. This argues that philosophy should study mathematics less as (potentially) concerning abstract entities, but rather as concerning the development of certain ideas. While Lautman pointed us to some excellent examples of this phenomenon, the Galoisian idea and the idea of duality, it seems less clear to me that they are situated somehow superior to mathematics as he believed.

We ended with a brief general discussion, which included a deliberately provocative comment from the philosopher John Kennedy that the majority of mathematicians don’t think hard enough about basic concepts of identity and relation, and that this marked an impoverishment of mathematics since the days of Hilbert.

It occurred to me just before I began my talk that I should have said more about Michael Harris’s comments, discussed at my old blog:

Perhaps we might find richer pickings in answering a challenge posed by Michael Harris in “Why Mathematics?” You Might Ask that philosophers “…have a duty, it seems to me, to account for terms like “idea” and “intuition” — and “conceptual” for that matter — used by human mathematicians (at least) to express their value judgments.” (p. 17). Take the term idea:

Nothing in the life of mathematics has more of the attributes of materiality than (lowercase) ideas. They have “features” (Gowers), they can be “tried out” (Singer), they can be “passed from hand to hand” (Corfield), they sometimes “originate in the real world” (Atiyah) or are promoted from the status of calculations by becoming “an integral part of the theory” (Godement). (p. 14)

Harris makes the very useful point that my own use of the term is liable to a certain slippage:

Corfield uses the same word to designate what I am calling “ideas” (“the ideas in Hopf’s 1942 paper”, p. 200) as well as “Ideas” (“the idea of groups”, p. 212) and something halfway between the two (the “idea” of decomposing representations into their irreducible components for a variety of purposes, p. 206). Elsewhere the word crops up in connection with what mathematicians often call “philosophy,” as in the “Langlands philosophy” (“Kronecker’s ideas” about divisibility, p. 202), and in many completely unrelated conections as well. Corfield proposes to resolve what he sees as an anomaly in Lakatos’ “methodology of scientific research programmes” as applied to mathematics by

a shift of perspective from seeing a mathematical theory as a collection of statements making truth claims, to seeing it as the clarification and elaboration of certain central ideas… (p. 181)

He sees “a kind of creative vagueness to the central idea” in each of the four examples he offers to represent this shift of perspective; but on my count the ideas he chooses include two “philosophies,” one “Idea,” and one which is neither of these. (p.16)

Point taken. I’ll see what I can do.

1. Hadi Zare - December 2, 2008

Hi,

I was there, and I thought I like to add this comment.

One I heard someone which said:

“Mathematics is what a mathematician does!”

Behind the discussions that this may not be a proper definition, however I think there is a sense of “truth” in this. For me, many people during time have found the language, and formality of mathematics useful for the type of science that they are doing. Very serious examples of this are coming from contributions that physicists and chemist have made. They have used mathematical symbols to express their own ideas, which perhaps not intentionally has added to mathematics itself.

If I may I would say that the philosophers in the meeting were a bit upset that the mathematics is gone far, and is not understandable for them. However, I would like to ask them “How many philosophers have tried to use maths to express their own ideas?”

Perhaps some will agree that our mind’s understanding is based on the notion of “difference”, and the appearance of this notion is quantification of the natural phenomenon. Maths is understandable for me, because I see thing, where in philosophy talk I see only a collection of words which are trying to describe and idea which may or may not be true, and there is not justification of them. That is why still philosophers find agreeing on things VERY DIFFICULT!

Thanks,