The Allen and Greenough is still under construction;
so some links may not work quite the way you would expect.
222. Conjunctions, like prepositions (cf. § 219), are closely related to adverbs, and are either petrified
cases of nouns, pronouns, and adjectives, or obscured phrases: as,
quod, an old accusative; dum, probably an old accusative (cf. tum, cum); véró, an old neuter ablative of
none the less; proinde, lit.
forward from there. Most conjunctions are connected with
pronominal adverbs, which cannot always be referred to their