I'm grappling with the prefix ad- in Latin. I don't know why, but I can't pinpoint its meaning. Or it just feels redundant. Here are some examples of my befuddlement.
The ad- in adduco feels redundant. I read its definitions below, and although written in English, none of them use "to" in English. And none of its meaning require or allude to the English preposition "TO".
I know that English is a Germanic, not Latinate, language. But in English, "ADduce" must be followed by "to". But then you've just used two functional morphemes meaning the same thing, "to"!
Allege is related to law, legal, legislation, legation, and litigation. Its original source was Vulgar Latin *exlitigāre, which meant ‘clear of charges in a lawsuit’ (from ex- ‘out of’ and litigāre ‘litigate’). This developed successively into Old French esligier and Anglo- Norman alegier, from where it was borrowed into English; there, its original meaning was ‘make a declaration before a legal tribunal’. Early traces of the notion of making an assertion without proof can be detected within 50 years of the word’s introduction into English, but it took a couple of centuries to develop fully.
The hard g of allegation suggests that though it is ultimately related to allege, it comes from a slightly different source: Latin allēgātiō, from allēgāre ‘adduce’, a compound verb formed from ad- ‘to’ and lēgāre ‘charge’ (source of English legate and legation).
Word Origins (2005 2e) by John Ayto, p 17 Right column.
Oxford Latin Dictionary (2012 2e), p 114 Center column. It lists "adduco" on p. 42 Centre column.