The zero conditional describes things that are always true or always happen. The pattern is simple: if plus present simple, then present simple. "If you heat ice, it melts." The result is not a plan and not an imagination. It is a fact.
Because the sentence is about a general truth, if and when often trade places: "When you heat ice, it melts" means the same thing. The zero conditional is the only conditional where this swap works without changing the meaning.
This page shows the pattern, the three jobs of the zero conditional, and how it differs from the first conditional. The 20-question drill at the end gives a rule reminder under every answer.
The rule
The pattern
- If plus present simple in the condition, present simple in the result: "If it rains, the streets get wet."
- The order can change without changing the meaning: "The streets get wet if it rains."
- When the if-clause comes first, add a comma. When it comes second, no comma is needed.
- Both halves stay in the present simple, even when the truth is timeless.
What the zero conditional does
- Scientific facts and natural laws: "If you mix red and blue, you get purple."
- Personal habits: "If I drink coffee after six, I cannot sleep."
- Rules and instructions: "If the alarm rings, leave the building."
- General truths about people and places: "If the sea is warm, swimmers stay longer."
If, when and unless
- If and when are both possible for general truths: "If the bus is late, I walk", "When the bus is late, I walk."
- When is better when the situation happens regularly and you expect it.
- Unless means if not: "Unless the weather changes, we play tennis."
- The main clause can also take an imperative: "If you see Ana, tell her the news."
Zero or first conditional?
- The zero conditional is about what always happens: "If it rains, I stay inside."
- The first conditional is about one real possibility in the future: "If it rains tomorrow, I will stay inside."
- Will never appears in the if-clause, even in the first conditional: "If it will rain" is wrong.
- Use the zero conditional for rules and routines, and the first for a single future event.
Small details that matter
- Do not use will or would in the if-clause of a zero conditional.
- An imperative in the result clause changes the job of the sentence to an instruction, and the pattern still works.
- With unless, the main clause stays positive: "Unless it rains, we walk."
- Use the present simple, not the present continuous, for eternal truths.
Examples
- If you heat water to 100 degrees, it boils.A scientific fact, so both halves use the present simple.
- When it snows, the roads get dangerous.When and if are both fine for general truths.
- If I eat too much sugar, I feel tired.A personal habit with a present simple result.
- If the door is locked, use the back entrance.A rule with an imperative in the result clause.
- Plants die if they get no light.The if-clause comes second, so no comma is needed.
- If you press this button, the machine stops.An instruction that describes what always happens.
- Unless you hurry, you miss the start of the film.Unless means if not and keeps the zero conditional pattern.
- If my sister calls, I always answer quickly.Always makes the repeated habit clear.
- Ice melts if you leave it in the sun.A natural law with the condition after the result.
- If the children are quiet, something is wrong.A joking general truth about a repeated situation.
Common mistakes
- Wrong: If you will heat ice, it melts. Right: If you heat ice, it melts.
- Will never appears in the if-clause. A general truth takes the present simple.
- Wrong: If it rains, the streets will get wet as a general fact. Right: If it rains, the streets get wet.
- For an always-true fact, both halves use the present simple. Will belongs to one specific future event.
- Wrong: If you heat ice, it will melts. Right: If you heat ice, it melts.
- Do not combine will with an -s verb form. The zero conditional simply uses the present simple.
- Wrong: Unless it does not rain, we walk. Right: Unless it rains, we walk.
- Unless already contains the negative, so does not is doubled.
- Wrong: If I am drinking coffee late, I cannot sleep. Right: If I drink coffee late, I cannot sleep.
- A habit takes the present simple, not the present continuous.
Practice drill
Answer all 20 questions. Each answer is marked at once, and the rule is explained under the question.
If you heat ice, it ___ .
Show answer and explanation
Answer: A. melts The zero conditional keeps the present simple in both halves for this general fact.
If I ___ coffee after six, I cannot sleep.
Show answer and explanation
Answer: B. drink A habit uses if plus the present simple in the zero conditional.
When it snows, the roads ___ dangerous.
Show answer and explanation
Answer: C. get When and if both take the present simple for an always-true result.
If the alarm rings, ___ the building.
Show answer and explanation
Answer: D. leave An instruction can use the imperative in the result clause of the zero conditional.
Plants die if they ___ no light.
Show answer and explanation
Answer: A. get The general fact keeps the present simple in the if-clause.
Unless you hurry, you ___ the train.
Show answer and explanation
Answer: B. miss Unless keeps the zero conditional pattern with the present simple for a general result.
If you press this button, the machine ___ .
Show answer and explanation
Answer: C. stops This describes what always happens, so both halves use the present simple.
If water ___ 100 degrees, it boils.
Show answer and explanation
Answer: D. reaches A scientific fact takes the present simple after if.
My brother always ___ if the film is funny.
Show answer and explanation
Answer: A. laughs The zero conditional result describes a repeated habit in the present simple.
If it ___ tomorrow, we will stay at home.
Show answer and explanation
Answer: B. rains This is the first conditional, so the if-clause still takes the present simple.
If the children are quiet, something ___ wrong.
Show answer and explanation
Answer: C. is A general truth uses the present simple in both halves of the zero conditional.
If you do not water plants, they ___ .
Show answer and explanation
Answer: D. die The sentence states a general fact, so the zero conditional keeps the present simple.
When the sun sets, it ___ dark.
Show answer and explanation
Answer: A. gets When introduces a general truth, and the result uses the present simple.
If my sister ___ , I always answer quickly.
Show answer and explanation
Answer: B. calls The habit takes the present simple in the if-clause of the zero conditional.
Unless it rains, we ___ outside.
Show answer and explanation
Answer: C. play Unless plus a general result keeps the zero conditional present simple.
If you mix red and blue, you ___ purple.
Show answer and explanation
Answer: D. get A mixing fact takes the present simple in the result clause.
If the bus ___ late, I walk to work.
Show answer and explanation
Answer: A. is The repeated habit uses the present simple after if in the zero conditional.
If you drop a glass on the floor, it ___ .
Show answer and explanation
Answer: B. breaks The result is always true, so the present simple breaks is correct.
If I ___ late, I skip breakfast.
Show answer and explanation
Answer: C. wake up A personal habit keeps the present simple in the zero conditional if-clause.
If you see Ana, ___ her the news.
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Answer: D. tell An instruction uses the imperative in the main clause of the zero conditional.
Drill complete
You answered every question.
Next topic: Mixed conditionals: past and present togetherTake the level test
Questions learners ask
What is the difference between if and when in the zero conditional?
For general truths, there is no real difference. If is a little more open, and when suggests the situation happens regularly. If you want to stress that the situation will certainly happen, choose when.
Can the result clause use the future?
Not for a general truth. If the sentence describes one future possibility, you have left the zero conditional and entered the first conditional: "If it rains tomorrow, I will take an umbrella." The zero conditional keeps both halves in the present simple.
Is the zero conditional only for science?
No. Science is one use, but habits, rules and instructions all follow the same pattern. "If I work late, I skip dinner" is as much a zero conditional as "If you boil water, it evaporates."
More grammar topics
Mixed conditionals: past and present together
When one half of a conditional looks at the past and the other at now, the sentence is mixed. The time words tell you which pattern you need.
Must vs have to: rules and obligations
Must is the obligation you feel or state. Have to is the obligation the world gives you. The two negatives mean completely different things.
May vs might: possibility and permission
May sounds a little more likely and a little more formal. Might sounds more remote and tentative. Both never take to.
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