Re: Bourbaki & category theory
I am ready to take back my criticism and apologize, if the "longer sentence" is correct. But is it? I am certainly not an expert in Bourbaki history, and, as far as I remember, they say no word about morphisms in the historical part of "Theory of Sets" and give no references on categories. But I think they "always" believed that structures determine isomorphisms but not morphisms, and I don't think they changed their mind between 1951 and 1957. When I say "they" I mean "those of them who made main decisions about the Bourbaki tractate". Because I hope (!) that not all of them were happy that categories are not even defined in the tractate. In my previous message I wrote "Removing Bourbaki's formalism..." but in fact that "formalism" is (not nice but) serious, in the sense that it takes us further away from abstract categories. Anyway, we need to know, if it is still possible, how exactly did Bourbaki definition of morphism(s) came up. George -------------------------------------------------- From: "Colin McLarty" <colin.mclarty@case.edu> Sent: Wednesday, May 23, 2012 1:06 AM To: "George Janelidze" <janelg@telkomsa.net> Cc: <categories@mta.ca> Subject: Re: categories: Re: Bourbaki & category theory
On Tue, May 22, 2012 at 5:51 PM, George Janelidze <janelg@telkomsa.net> wrote:
Dear Colleagues,
I don't think it is good to say that "Bourbaki had a notion of isomorphism but no general notion of morphism", even in a brief message!
It would not be good -- unless it was part of a longer sentence.
I wrote "Prior to encountering category theory, Bourbaki had a notion of isomorphism but no general notion of morphism." The Bourbaki passage you quote was first published in 1957, at least 6 years after Bourbaki encountered category theory as shown by the letter from Weil that i quoted.
best, Colin
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It seems to me that all this discussion concerning whether the notion of isomorphism comes before of that of morphism or the other way around, or if Bourbaki had it or not, is meaningful only on historical basis. The notion of category as an abstraction of the notion of morphism would had been forgotten and it would have disappear from mathematical practice. What happened, as an unexpected consequence of the definition of category, was that the notion of universal property found its home, and may be this is what Bourbaki, which already had the notion of universal property, missed (I say may be). This we can see it from the beginning of the first substantial contributions of categories to mathematics, as for example in the work of Kan on adjoint functors, or in the fact that a trivial statement as Yoneda's Lemma is the most important fact in Category Theory. e.d. On 23/05/12 08:36, George Janelidze wrote:
I am ready to take back my criticism and apologize, if the "longer sentence" is correct. But is it?
I am certainly not an expert in Bourbaki history, and, as far as I remember, they say no word about morphisms in the historical part of "Theory of Sets" and give no references on categories. But I think they "always" believed that structures determine isomorphisms but not morphisms, and I don't think they changed their mind between 1951 and 1957.
When I say "they" I mean "those of them who made main decisions about the Bourbaki tractate". Because I hope (!) that not all of them were happy that categories are not even defined in the tractate.
In my previous message I wrote "Removing Bourbaki's formalism..." but in fact that "formalism" is (not nice but) serious, in the sense that it takes us further away from abstract categories.
Anyway, we need to know, if it is still possible, how exactly did Bourbaki definition of morphism(s) came up.
George
[For admin and other information see: http://www.mta.ca/~cat-dist/ ]
On Wed, May 23, 2012 at 7:36 AM, George Janelidze <janelg@telkomsa.net> wrote:
I am ready to take back my criticism and apologize, if the "longer sentence" is correct. But is it?
Yes, it is. I am an expert on Bourbaki history. See my articles on Chevalley, Dieudonné, and Weil in the New Dictionary of Scientific Biography. As Eduardo says, it is a historical question. Here are the historical facts Bourbaki's first publication was Bourbaki, N. [1939]: Th{\'e}orie des ensembles, Fascicules de r{\'e}sultats, Paris: Hermann, Paris. It is very sketchy on "structures," and uses no notion of mapping between structures except isomorphisms. Their actual theory of structures first appeared in Bourbaki, N. [1957]: Th{\'e}orie des ensembles}, Chapter 4, Paris: Hermann. That theory was a rear-guard action meant to give an alternative to category theory. As i mentioned before, Weil was citing the categorical idea, and thinking about finding an in-house alternative to it, already in 1951. By 1957 Grothendieck, and Cartier, and Chevalley, probably Dieudonne, and others, all saw that category theory was more agile than these structure, simpler, and more to the point, plus it had a natural "higher order" aspect in the theory of functors which was actually more useful in practice than categories alone. Cartier has justly said it would have been a huge job to formulate all Bourbaki's ideas in terms of categories and functors. It would have called for a lot of ideas which were only invented in the coming years. It was relatively easy to give Bourbaki's theory of structures -- because it never really worked at all even for Bourbaki's purposes (as Corry documents in detail). Naturally it is easier to give an unusable theory of structures than to work out the ways categories and functors would actually be used. best, Colin
I am certainly not an expert in Bourbaki history, and, as far as I remember, they say no word about morphisms in the historical part of "Theory of Sets" and give no references on categories. But I think they "always" believed that structures determine isomorphisms but not morphisms, and I don't think they changed their mind between 1951 and 1957.
When I say "they" I mean "those of them who made main decisions about the Bourbaki tractate". Because I hope (!) that not all of them were happy that categories are not even defined in the tractate.
In my previous message I wrote "Removing Bourbaki's formalism..." but in fact that "formalism" is (not nice but) serious, in the sense that it takes us further away from abstract categories.
Anyway, we need to know, if it is still possible, how exactly did Bourbaki definition of morphism(s) came up.
George
[For admin and other information see: http://www.mta.ca/~cat-dist/ ]
participants (3)
-
Colin McLarty -
Eduardo J. Dubuc -
George Janelidze