Advanced Unit 7
Advanced · Grammar Reference
Unit 7 — Real and Unreal Tense Usage
first · second · third conditionals · mixed · wish/hypothesizing · would
7.1  First conditional sentences (real)

It is important to understand this difference between fact and non-fact when discussing conditional sentences.

7.2  Second conditional sentences (unreal)
7.3  Third conditional sentences (unreal)

Third conditional sentences, like the Second, are not based on fact. They express a situation which is contrary to reality in the past. This unreality is shown by a tense shift 'backwards': Past → Past Perfect, would → would have.

If I had known his background, I would never have employed him.If I hadn't seen it with my own eyes, I wouldn't have thought it possible.
7.4  Second and Third mixed

It is possible for each of the two clauses in a conditional sentence to have a different time reference, and the result is a mixed conditional.

If we had brought a map with us, we would know where we are.If I didn't love her … is contrary to present fact (I do love her). I wouldn't have married her … is contrary to past fact (I did marry her).
7.5  Hypothesizing about the present and future

The Past Simple tense form is used for present and future time reference. Note that were is often used instead of was, especially in formal style.

I wish I were taller!   If only he were here now!
Present state v. present action or event

When we hypothesize about a present state, the Past Simple tense form is used.

I wish you lived nearer.   If only I had a car!

When we hypothesize about a present action or event, would is used.

I wish you'd help more in the house.   If only she wouldn't wash her socks in the bath!
📌 Note
Would here expresses willingness in the first sentence, and annoying habit in the second.
Notice that it is unusual to say I wish/If only I wouldn't … because we can control what we want to do. However, we can say I wish/If only I could …
We can say I wish/If only … would to refer to a definite time in the future, but only if we think that the action will probably not happen: I wish she'd come with me tomorrow.
7.6  Hypothesizing about the past

The Past Perfect tense form is used for past time reference.

I wish she hadn't been so unkind.If only the police had looked in the attic, they would have found him!
Fact v. non-fact
Fact
He looked as if he was tired. (= this is probably how he felt.)
Non-fact
He looked as if he had seen a ghost. (Non-fact — very improbable.)
would like

Would like can be used with a perfect infinitive to talk about things we wish we had done.

I would like to have lived in the eighteenth century.

This can also be expressed by would have liked followed by either an ordinary infinitive or a perfect infinitive.

7.7  would