How did 'to wit' shift (from "to know") 🡺 to mean 'that is to say'?


Unquestionably, "wit" or "knowing" are concepts distinguishable from "saying". Thus how did 'that is to wit' shift 🢂 to denote 'that is to say; namely'?


Both the noun wit [OE] and the verb [OE] go back ultimately to the Indo-European base *woid-, *weid-, *wid-. This originally meant ‘see’, in which sense it has given English visible, vision, etc, but it developed metaphorically to ‘know’, and it is this sense that lies behind English wit. The noun to begin with denoted ‘mind, understanding, judgement, sense’ (a meaning preserved in expressions such as ‘keep one’s wits about one’ and ‘slow-witted’), and the modern sense ‘clever humorousness’ did not begin to emerge until the 16th century. The verb has now virtually died out, except in the expression to wit. Witness is etymologically the state of ‘knowing’. Other English words that come from the same Indo-European base or its Germanic descendant include guide, history, idea, story, and twit.

Above — John Ayto, Word Origins (2005 2e), p 549 Left column. Below — Etymonline on the verb "wit":

"to know" (archaic), Old English witan (past tense wast, past participle witen) "to know, beware of or conscious of, understand, observe, ascertain, learn,"
from Proto-Germanic *witanan "to have seen," hence "to know" (source also of Old Saxon _witan_, Old Norse _vita_, Old Frisian _wita_, Middle Dutch, Dutch _weten_, Old High German _wizzan_, German _wissen_, Gothic _witan_ "to know"), from PIE root *weid- "to see."

The phrase to wit, almost the only surviving use of the verb, is first recorded 1570s, from earlier that is to wit (mid-14c.), probably a loan-translation of Anglo-French cestasavoir, used to render Latin videlicet (see viz.).
  • I suppose the closest current equivalent is Just So You Know - Wikipedia
    It's rather something between “namely” and “I mean” – it presents the information as ideally already known to the addressee, and is thus very different from the confiding “just so you know”. “namely” probably initially had a tone of avoiding hints and circumlocutions and getting straight to the point.
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    Thus how did 'that is to wit' shift 🢂 to denote 'that is to say; namely'?
    I consider this interpretation wrong or at least misguided. To wit and that is to say are two alternative set phrases that can be used for the same purpose, namely to introduce a clause that explains a general term more precisely and narrows it down to a specific case of this general term. You cannot deduce from this that the verbs wit and say as such linked semantically. Only the complete set phrases are linked and only through this common function, which again does not constitute a direct semantic link.