Used for scientific facts, universal truths, and automatic habits.
If you heat ice, it melts • Water boils if it reaches 100°C
If you don't water plants, they die
What happens if you mix red and yellow?
In Zero Conditional, IF and WHEN have the exact same meaning.
When the sun sets, it gets dark
When it doesn't rain, grass turns brown
When does water freeze?
| Example / Question | Positive / Short Answer | Negative / Short Answer |
|---|---|---|
| Scientific Fact: Ice melting | If you heat ice, it melts. | Both sides Present Simple |
| Automatic Habit: Headaches | If I drink coffee late, I get a headache. | Cause & Effect habit |
| Comma Rule | If clause first → USE comma | Main clause first → NO comma |
| Rule | Base / Standard Form | Applied Form |
|---|---|---|
| Present Simple in Both Clauses Rule | Zero conditional MUST use Present Simple in BOTH the condition clause and the main clause! | If it rains, grass gets wet (NOT "will get wet") |
| If = When Equivalence Rule | In Zero Conditional, IF can be substituted with WHEN without any change in meaning. | If you heat ice = When you heat ice |
| Comma Punctuation Rule | If the IF-clause comes first, place a comma after it. If main clause is first, no comma is needed. | If it rains, stay inside vs Stay inside if it rains |
Express physical rules that are always 100% true.
Describe how you always react to a specific trigger.
Explain how devices or systems work.
Zero Conditional expresses 100% general scientific facts/habits (If + Present, Present). First Conditional expresses real SPECIFIC future possibilities (If + Present, WILL + V1).
Yes! E.g., "If you feel sick, CALL a doctor." (Imperative in main clause is very common).
Yes! In Zero Conditional, both mean "every time that" something happens.