The Latin preposition de takes an ablative object and has several different translations including 'about', 'of', 'down from' and 'from'. The preposition a/ab also has multiple meanings including 'after', 'by' and 'from'.
Both words can mean 'from'. When the meaning of the word is 'from', is there a difference in usage or meaning and is it preferable to use one over the other?
Like all good questions, this one has no simple answer. The big dictionaries devote many columns to it. Kennedy 286 gives a crisp & useful summary. A couple of firm examples:
Travelling from a place... is ab.
I am of or from the family X... is de.
Nearly always, ab is elided to a before a consonant. See the Oxford Latin Dictionary for exceptions.
A place-holder, until someone writes the perfect answer. Rule of thumb rules:
Avoid an elision or a hiatus by choosing 'ab,' 'abs', in preference to 'a' or 'de.'
ab urbe.
Where 'from' can be replaced by 'down from', pick 'de'
de montibus cucurrit. de turris autem versus concino.
