Page 116 - Practical English Usage 3ed - Michael Swan, Oxford

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before (preposition) and in front of 98 He did military service before he went to university.
(He did military service first.)
present tense with future meaning
With before, we use a present tense if the meaning is future (see 580). I'll telephone you before I come. (NOT •.• be}fJFe : will Mtne.)
perfect tenses
In clauses with before, we often use present perfect and past perfect tenses to emphasise the idea of completion.
You can't go home before I've signed the letters. (= •.. before the moment when I have completed the letters.)
He went out before I had finished my sentence. (= ... before the moment when I had completed my sentence.)
(Note that in sentences like the last, a past perfect tense can refer to a time later than the action of the main verb. This is unusual.)
before things that don't happen
We sometimes use before to talk about things that don't happen (because something stops them).
We'd better get out of here before your father catches us. She left before I could ask for her phone number.
before . . .ing
In a formal style, we often use the structure before . . .ing. Please put out all lights before leaving the office.
Before beginning the book, she spent five years on researcll.
For before as an adverb and preposition. see 96. 98.
before (preposition) and in front of
before: time
in front of: place
Compare:
I must move my car before nine o'clock.
It's parked in front ofthe post office. (NOT ••. be;~Fe the "Mt Bjfiee.)
Before is normally used to refer to time. However, it can refer to place: a to talk about order in queues, lists, documents etc
Do you mind? I was before I in front ofyou!
Her name comes before mine in the alphabet.
We use 'a' before a consonant and 'the' before a vowel.
b to mean 'in the presence of (somebody important)'
I came up before the magistrates for dangerous driving last week.
c in the expressions right before one's eyes, before one's very eyes.
For the difference between in front ofandfacinglopposite, see 402. For before as an adverb and conjunction, see 96-97.
For by meaning 'allon or before', see 117.
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