What is purple and commutes?

An abelian grape

Also, I think there's sometimes a semantic difference between the 'zero-derived' modifier and the ones with an explicit derivational morpheme. For example, 'Bayesian' refers to a set of tools or school of thought in statistics, whereas 'Bayes' as a modifier refers to precise decision-theoretic concepts like Bayes risk, Bayes rule (this 'Bayes' can also be predicative: 'The rule is Bayes'), etc.

@Peter Erwin: Even in linguistics, we have some examples, particularly in quantitative and computational linguistics, e.g. the Zipf-Mandelbrot Law I mentioned above, the Silverstein hierarchy, the Keenan-Comrie hierarchy (another name for the NP accessibility hierarchy of Keenan and Comrie (1977)), Chomsky normal form, the Menzerath-Altmann Law, Kneser-Ney smoothing, etc.

]]>cameron: There's also "the effect of Hanbury-Brown and Twiss", preferred by people like me, who talk loudly in restaurants, I mean who like to hyphenate compound modifiers.

Haamu: And

*"She read a Yeats."

*"She read the Yeats."