[FOM] category theory as the analysis of symmetry
paul at personalit.net
Wed May 3 18:45:51 EDT 2017
[NOTE: Includes corrections.]
Recent FOM discussion is evidence that category theory has a
foundational role to play in mathematics.
For example, transformational grammar represents a sentence S in terms
of conjoining a noun phrase NP and a verb phrase VP, i.e. (NP + VP) = S.
Here, (NP + VP) expresses a symmetric relation R such that R(NP, VP)
mutually implies R(VP, NP).
The * in group theory is another example.
But another way to represent the fact that (NP + VP) = S is as NP --> VP
--> S, which is distinct from VP --> NP --> S, as grammarians well know.
The difference is that the arrows --> express both inheritance and
transformation, but not the symmetric representation (VP + NP) = S.
The arrow --> is DIACHRONIC, while symmetric operators like + and * are
Therefore, category theory is the general analytical tool or organon for
interpreting symmetric relations like (NP + VP) into distinct maps (NP
--> VP) and (VP --> NP), even when the analysis is syncategorematic, as
with transformational grammar.
Using category theory, a diagram like the square of opposition becomes a
logic of implication, contradiction and contrariety for A,E,I,O
expressions, like Aristotle's syllogistic.
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