A practical english grammar - Vyssaja skola 1978

Clauses of time
Sound symbols

Time clauses are introduced by one of a limited number of words or phrases: when, while, as, before, until, since, after, as soon as, and a few others. The clause is placed before or after the main clause at the option of the speaker.

Please look at this letter before you go out.

Before you go out, please look at this letter.

A time clause that deals with events in the future has its verb in the plain present tense or in the present perfect. Will is never used in time clauses in English.

I’ll tell him when he comes.

After you have eaten, let’s go to the park.

You’d better write down the number before you forget it.

I’m going to work on this lesson until I’ve learned it.

The action, or the completion of the action, of all of the time clauses in the examples just given lies in the future. When the future is viewed from a standpoint in the past, the appropriate change of tense is made.

I promised that I would tell him when he came.

I suggested that we go to the park after he had eaten.

Sometimes time clauses are introduced by nouns, with or without a connecting word (that or sometimes when). .

The moment he learned the truth, he resigned.

I saw them the day I left for Europe.

We were there the week that it snowed so heavily.

The past perfect, as we saw in Chapter 6, is used to show that one of two events in the past was earlier than the other. Instead of the past perfect, the simple past is often used, if no ambiguity would result.

After she put the bread in the oven to bake, she began to set the table.

The use of after makes it clear that putting the bread in the oven is an earlier event than setting the table. If when had been used, however, the past perfect would have been required, since when may mean either that the completion of one action is the occasion for the other, or that they occur at the same time.

When the baby saw its mother, it smiled broadly.

When we had finished eating, we left the table.

When she had put the bread in the oven to bake, she began to set the table.

When also means “every time that” and overlaps with whenever.

When (or Whenever) I read too long, I get a headache.

When often means “and then.”

I had just gone to bed when the telephone rang.