Basically, conditional sentences are used to talk about:

1/ A situation which sometimes exists or existed:

If they lose weight during an illness, they soon regain it afterwards.

If he saw me in the street, he’d just say ‘Good morning.’

2/ A situation which you know it does not exist:

If England had a hot climate, the attitude would be different.

3/ A situation which you don’t know whether it exists or not:

If he is right, it would be possible once more to manage the economy in the old way.

4/ A situation which may exist in the future:

If I marry her, we shall need the money to live on.

Unless: means ‘If…not’. Eg: You will fail your exam unless you work harder (If you don’t work harder).

Modals and Imperatives:

- Using a modal in the main clause to talk about a situation which does not exist:

If anybody had asked me, I could have told them what happened.

- With imperative structure:

If you understand this problem, show me how to do it.

If somebody calls today, tell me at once.

Tenses in conditional sentences:

TYPE 1: Future Conditionals

TYPE 2: Present Conditionals

TYPE 3: Past Conditionals

In fact, as sense and context permit, any tense sequence is possible:

TYPE 1 – TYPE 3:

If I am as clever as you think, I should have been rich by now.

TYPE 2 – TYPE 3:

If you knew me better, you wouldn’t have said that.

TYPE 3 – TYPE 2:

If I had had your advantages, I would be better off now.

TYPE 2 – TYPE 1:

If he missed the bus, he won’t be here on time.

Factual Conditional Sentences:

1. Generic Factual Conditionals express relationships that are true and unchanging:

If oil is mixed with water, it floats.

If you boil water, it vaporizes.

2. Habitual Factual Conditionals resemble generic factual conditionals in that they also express a relationship that is not bounded in time. However, the relationship is based on habit instead of physical law. Habitual factual conditionals express either their past or present relationships that are typically or habitually true:

Present: If I wash the dishes, Sally dries them.

Past: If Nancy said, ‘Jump!’ Bob jumped.

‘IF’ is possible substituted by ‘when’ or ‘whenever’:

When(ever) you boil water, it vaporizes.

When(ever) I wash the dishes, Sally dries them.

3. Implicit Inference Factual Conditionals express inferences about specific time-bound relationships. As such, they make use of a much, a wider range of tense and aspect markers and they also occur with certain modal auxiliaries:

If it is raining out there, my motorbike is getting wet.

If there was any happy man in the world that night, it was John Turney.

If you’ll bring some wine, I’ll bring some beer and potato chips.

4. Explicit Inference Conditional is the only case where there is no strict parallelism of tense, aspect, or modal in both clauses. This is because the condition is used as the basis for making an explicit inference:

If someone’s at the door, it must be Peter.

If someone has the answer, it should be Rod.

- Implicit inference: If it is raining out there, my car is getting wet.

- Explicit inference: If it is raining out there, my car must be getting wet.

- Past implicit inference: If he was there, he saw the painting.

- Past explicit inference: If he was there, he must have seen the painting.

Future (or Predictive) Conditional Sentences: express future plans or contingencies.

If-clause: Simple Present Tense – Result clause: will/be going to…(Sometimes: may/should)

If it rains, I’ll stay home.

If you finish your homework, I’m going to buy you an ice-cream.

If you finish your homework, I may buy you an ice-cream.

Imaginative Conditional Sentences:

- Hypothetical Conditionals: express unlikely yet possible events or states:

If I had enough money, I would buy a car. (not a strong negation here. There is an outside chance that the speaker has)

- Counterfactual Conditionals: express impossible events or states. Refer to the present or the past:

Present: If I were the Prime Minister, I would make some changes.

Past: If I had been the Prime Minister, I wouldn’t have made that decision.