Latin mecum, tecum, etc.

[petegray]

>"whereof," "whereas" and "therefore."
> Are these imitations or calques on Latin forms?

Note the interesting survival of one of these forms in the Word
spell-checker, which offers you both "therefore" and "therefor".    The
latter (at least in the English I know) can only mean "for it".

They don't reflect Latin forms at all, but they are clearly seen in modern
German.   In that language in general:

    Preposition + [some case of "it"]  --> da (= "there") + preposition

    Preposition + [some case of "which"]  --> wo (= "where") + preposition

In both cases haitus between vowels is avoided by inserting "r".

For example:
       from it  (von-)  = davon  =  da-von  = therefrom
       for it     (fuer)   =  dafuer  = da-fuer  = therefor  (not
"therefore")
        on it  (auf)      =  darauf  = da-r-auf  = thereon

    from which = wovon  = wherefrom
    for which = wofuer  =  wherefor
    on which  =  worauf  = wo-r-auf  = whereon.

These are very regular in German.   There are survivals of this construction
in English in words such as "whereupon" and "whys and wherefors"

Peter