Many short words can act as different parts of speech: prepositions, conjunctions, adverbs or pronouns. The words here are more or less grouped grammatically, but strict grammatical analysis is not our purpose; clarity is.

Prepositions following verbs and adjectives

Grammar dictates when a word is a preposition, but it doesn’t help much with knowing which preposition to use, because usage and idiom are more important than grammar. Usage is changing the meaning of compare to (from its meaning of liken, see p. 66), and idiom (COD: a group of words having a meaning not deducible from those of the individual words) dictates the different meanings of set about, set in, set off and set up.

It would be nice to refer to a set of rules that govern prepositions, but there isn’t one. Native speakers usually know instinctively what is right, but even they get it wrong sometimes; EAL writers have to learn it. The Swedish pop group, Abba, sang, ‘Now we’re old and grey Fernando, since many years I haven’t seen a rifle in your hand.’ There is no simple way of explaining why the correct preposition is for rather than since. (See Ch. 17.)