Naturality as compatible comparison of functors
Research context
postgraduate concept · established · As of 2026-10-10
A natural transformation eta:F⇒G assigns a morphism eta-X:F(X)→G(X) to every object so that G(f) eta-X=eta-Y F(f).
Key knowledge
A natural transformation eta:F⇒G assigns a morphism eta-X:F(X)→G(X) to every object so that G(f) eta-X=eta-Y F(f). For vector spaces the map into the double dual is natural: a vector evaluates linear functionals, compatibly with every linear map. It is an isomorphism for finite-dimensional vector spaces, while infinite-dimensional algebraic double duals can be larger.
Values and equations
G(f) o eta_X = eta_Y o F(f)
- F,G
- Functors from C to D
- f
- Morphism X to Y in C
- eta_X
- Component of the natural transformation
Conditions and scope
- The naturality square is required for every morphism, not merely for a chosen basis.
- The double-dual example uses algebraic duals; continuous Banach dual reflexivity is a different question.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: §§1.1–1.4 categories/functors/naturality, §2.2 Yoneda, chapter 4 adjunctions. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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