This document summarizes the forms and uses of three types of conditional sentences in English:
Type 0 or universal conditional uses "if" with the present or imperative form to describe scientific facts or instructions. Type 1 or first conditional uses "if" with the present and "will" to describe likely results or promises/warnings. Type 2 or second conditional uses "if" with the past simple and "would" to describe improbable or hypothetical situations.
2. TYPE ZERO / UNIVERSAL
FORM
IF + Present,
Present / Imperative
USE
True / scientific facts
Instructions
EXAMPLES
If you put paper on a fire, it burns
If the phone rings, answer it
3. FIRST CONDITIONAL (TYPE 1)
FORM
IF + Present,
WILL (Must / can / may)
USE
Likely / probable results
Promises, warnings, threats
EXAMPLES
If we dont leave now, well miss the train
If you pass your exam, Ill give you a job
4. SECOND CONDITIONAL (TYPE 2)
FORM
IF + Past simple,
WOULD (Could / Might)
USE
Unreal/Improbable situations
(Conditions wont be met)
Advice / suppositions contrary to known facts
EXAMPLES
If you did more exercise, youd feel better
If I were you, I wouldnt drive so fast
5. NOTES
If I were you (Written / formal language)
If I were / was you (spoken language)
If he / she / it were (more usual)
If he / she / it was (more colloquial)
6. GENERAL FACTS
We can exchange the order of the clauses
If you go, Ill go
Ill go if you go
Connectors
UNLESS = IF NOT
You wont pass if you dont study
You wont pass unless you study