Why is C-selection called 'subcategorisation' and not only 'categorisation'?

Question

_{Source: p 94, An Introduction to Language (10 ed, 2014) by V Fromkin, R Rodman, N Hyams}

The information about the complement types selected by particular verbs and other lexical items is called C-selection or subcategorization, and is in cluded in the lexical entries of the items in our mental lexicons. (C stands for "categorial.")

I am curious why subcategorization (with its prefix 'sub-') was selected, while C-selection uses only the stem "categorial" in referring to Grammatical/Syntactic Categories (not Subcategories).
The OED does not disambiguate.

Answer 1

I'm not familiar with the term "C-selection". Taking categories to be NP, V, P, ..., when these categories are divided up (as they must be) into, e.g., singular and plural NPs (NPpl, NPsg), and transitive and intransitive verbs (Vtr, Vin), that is referred to as subcategorization.

There is no grammatical theory, so far as I know, that provides any basis for a distinction between the two sorts of terminological splits. It's just a matter of what is convenient and what is usual and customary.

In Aspects of the theory of syntax, Chomsky used the term "strict subcategorization" to refer to the subdividing of major categories like N or V, into subcategories according to what tree sisters (also with parents NP or VP, resp.) they could cooccur with, e.g. Vtr or Vin. The restriction to tree sisters was intended to have theoretical significance.