ab

"ab" takes the ABLATIVE and means "away from", starting at the outside of something, in contrast to "ex", which starts inside it, and "de", which comes down off it. It also marks a starting point in time, as in "ab initio", from the beginning.

Its other job is the important one for reading: with a PASSIVE verb, "a" or "ab" plus the ablative names the person doing the action. "A patre missus est" is "he was sent by his father". If the doer is a thing rather than a person, Latin drops the preposition and uses the bare ablative instead, so a city destroyed by fire is "igni deleta" with no "ab" in sight.

The short form "a" stands before consonants and "ab" before vowels and h, with "abs" surviving in a few fixed phrases.