The zero conditional describes something that is always true: whenever the condition happens, the result happens. It's used for scientific facts, general rules, and personal habits that never change.
Both clauses use the present simple.
The condition and the result are tied together as a constant rule, not a one-time event.
Form
The structure is symmetrical — present simple on both sides.
| IF-CLAUSE (CONDITION) | MAIN CLAUSE (RESULT) |
|---|---|
| if + present simple | present simple |
A few clean examples:
The if-clause sets the trigger; the main clause states what always follows.
What it's used for
Three typical kinds of statements fit the zero conditional.
Scientific and physical facts.
General rules and routines.
Personal habits that are always true.
The situation can apply to the whole world (water boils at 100°C) or just to one person (Maria always calls on Sunday). What matters is that the pattern is consistent.
If and when
In the zero conditional, if and when are interchangeable. Both describe a rule that always applies, so the meaning doesn't change.
This only works in the zero conditional. In other conditionals, if and when mean different things, so the swap is safe only when the statement describes something that always happens.
Order of clauses
The if-clause can come first or second. The meaning stays the same.
When the if-clause comes first, use a comma:
When it comes second, no comma:
This is the standard rule for all conditionals.
Giving instructions
The zero conditional often gives instructions or advice. In that case, the main clause uses the imperative instead of a present simple verb.
The logic is the same — a condition plus a constant response — but the response is a command rather than a statement of fact.
Zero vs. first conditional
Both start with if + present simple, so they are easy to confuse. The difference is in the main clause.
| CONDITIONAL | MAIN CLAUSE | MEANING |
|---|---|---|
| Zero | present simple | Always true |
| First | will + verb | Specific future event |
Compare:
Use the zero conditional for general patterns. Use the first conditional when you're talking about one particular future situation.
Common mistakes
Will in the if-clause
Will in the main clause (mixing with first conditional)
Continuous instead of simple
Comma placement
Wrong imperative form