Conditional sentences, if-clauses type I, II, III

Conditional sentences

Conditional sentences are sometimes confusing for learners of English as a second language.

Watch out:

  1. Which type of conditional sentences is it?
  2. Where is the if-clause (e.g. at the beginning or at the end of the conditional sentence)?

There are three types of conditional sentences.

type condition
I condition possible to fulfill
II condition in theory possible to fulfill
III condition not possible to fulfill (too late)

1. Form

type if-clause main clause
I Simple Present will-future or (Modal + infinitive)
II Simple Past would + infinitive *
III Past Perfect would + have + past participle *

2. Examples (if-clause at the beginning)

type if clause main clause
I If I study, I will pass the exam.
II If I studied, I would pass the exam.
III If I had studied, I would have passed the exam.

3. Examples (if-clause at the end)

type main clause if-clause
I I will pass the exam if I study.
II I would pass the exam if I studied.
III I would have passed the exam if I had studied.

4. Examples (affirmative and negative sentences)

type   Examples
    long forms short/contracted forms
I + If I study, I will pass the exam. If I study, I'll pass the exam.
- If I study, I will not fail the exam.
If I do not study, I will fail the exam.
If I study, I won't fail the exam.
If I don't study, I'll fail the exam.
II + If I studied, I would pass the exam. If I studied, I'd pass the exam.
- If I studied, I would not fail the exam.
If I did not study, I would fail the exam.
If I studied, I wouldn't fail the exam.
If I didn't study, I'd fail the exam.
III + If I had studied, I would have passed the exam. If I'd studied, I'd have passed the exam.
- If I had studied, I would not have failed the exam.
If I had not studied, I would have failed the exam.
If I'd studied, I wouldn't have failed the exam.
If I hadn't studied, I'd have failed the exam.

* We can substitute could or might for would (should, may or must are sometimes possible, too).

  • I would pass the exam.
  • I could pass the exam.
  • I might pass the exam.
  • I may pass the exam.
  • I should pass the exam.
  • I must pass the exam.

Thanks to Kai.