All this work culminated in another notion, thanks to Grothendieck and his school: that of a topos. Even though toposes appeared in the 1960s, in the context of algebraic geometry, again from the mind of Grothendieck, it was certainly Lawvere and Tierney’s (1972) elementary axiomatization of a topos which gave impetus to its attaining foundational status. Very roughly, an elementary topos is a category possessing a logical structure sufficiently rich to develop most of “ordinary mathematics”, that is, most of what is taught to mathematics undergraduates. As such, an elementary topos can be thought of as a categorical theory of sets. But it is also a generalized topological space, thus providing a direct connection between logic and geometry. (For more on the history of categorical logic, see Marquis & Reyes 2012, Bell 2005.)
Categories, functors, natural transformations, limits and colimits appeared almost out of nowhere in a paper by Eilenberg & Mac Lane (1945) entitled “General Theory of Natural Equivalences.” We say “almost,” because their earlier paper (1942) contains specific functors and natural transformations at work, limited to groups. A desire to clarify and abstract their 1942 results led Eilenberg & Mac Lane to devise category theory. The central notion at the time, as their title indicates, was that of natural transformation. In order to give a general definition of the latter, they defined functor, borrowing the term from Carnap, and in order to define functor, they borrowed the word ‘category’ from the philosophy of Aristotle, Kant, and C. S. Peirce, but redefining it mathematically.
I thought Perplexity did a good job answering my question about whether the idea of a functor was analogous to an analogy, making “natural transformation” mean “analogous analogies”.
I liked that as a specific example it featured the hydraulics-to-electronics analogy, as being of the functor type.
Functors are akin to translations between natural languages, giving rise to different ways of expressing the “same thing”.
Natural language processing (NLP) makes analogous analogies a central focus, seeking to encode the generic essence of relationships in a generalized semantics. I sound like a chatbot now. I’m shaking my rattle.
A natural transformation takes us from one analogy to another (a meta-functor).
A phrase which stuck with me, an analogy of sorts: “toposes could prove to be for the 21st century what Lie groups were to the 20th century.”
Both provide overarching schemas, conceptual frameworks, inside of which more specific systems (of concepts) do their thing. Conventionally such overarching schemas are called “foundations” but if we zoom out to just see “in-falling to form a spherical network” then our “foundation” is more like a “spaceship” (freely floating).
When used to characterize a specific mathematical domain, category theory reveals the frame upon which that area is built, the overall structure presiding to its stability, strength and coherence. The structure of this specific area, in a sense, might not need to rest on anything, that is, on some solid soil, for it might very well be just one part of a larger network that is without any Archimedean point, as if floating in space. To use a well-known metaphor: from a categorical point of view, Neurath’s ship has become a spaceship.
I’ll be pestering Perplexity about Neurath’s ship.











