The perfect conditional tense.

This is formed with would / should and the perfect infinitive:

Affirmative I would/ should have worked

you would have worked etc.

Negative I would not/ I should not have worked etc.

Interrogative would/ should I have worked? etc

Negative interrogative should I not have/ shouldn’t I have worked?

would you not have/ wouldn’t you have worked? etc.

§ 19.

CONDITIONAL SENTENCES.

A conditional sentence usually has two clauses, a main clause and a subordinate conditional clause. We use conditional sentences to imply that the events of the main clause depend upon those of the conditional clause. So:

Conditional clause main clause

If I can produce the letter … the matter will be forgotten.

The speaker means that his employers will forget that he has lost a certain letter if (only if) he can show them it. But if he is unable to produce it, his carelessness will not be forgotten.

§ 20.

UNLESS

Most conditional clauses start with if, they are often called if -clauses. Unless is the negative form of if and means only if not:

If I can’t produce it … ~ Unless I can produce it …

We often use unless in threats (a) and warnings (b).

(a) Unless you stop making that noise, I’ll scream!

(b) You’ll be hungry later unlessyou eat now.

Not all negative if sentences can be transformed into unless sentences.

If he wasn’t told by Jane, he couldn’t have known. ~ Unless he was told by Jane, he couldn’t have known. (can be changed)

If Mr. Smith doesn’t come back, I’ll phone you. (cannot be changed)

Other possible subordinators include: as / so long as, provided / providing that (= but only if), on condition that, even if / even though. If one situation depends on another, if can be replaced by as / so long as, provided / providing that. To introduce questions suppose / supposing (that) …? (~ What if …?) can be used.

You can borrow my camera as long as you are careful with it.

I’ll go to the party providedyou go too.

Suppose he himself gave her the injections …

§ 21.

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