The zero is used for facts, rules and results that are always true. The form is if plus the present simple, then the present simple: If you heat ice, it melts. You can usually replace if with when and the meaning stays the same.
The form
A zero sentence has two parts. The if clause gives a condition. The main clause gives the result. Both parts use the present simple.
If + present simple, present simple. If the temperature drops below zero, water freezes. If people eat too much sugar, they put on weight.
The two clauses can change places. When the if clause comes first, put a comma after it. When the main clause comes first, you do not need a comma: Water freezes if the temperature drops below zero.
- If you heat ice, it melts. · Ice melts if you heat it.
- If traffic increases, air quality gets worse. · Air quality gets worse if traffic increases.
When to use it
Use the zero when the result always follows the condition. It is the conditional of facts, rules and habits. It does not talk about one future event. It talks about what is generally true.
In IELTS, you can use it for scientific facts (If you mix red and blue paint, you get purple), general social truths (If young people have no job, they often depend on their families), and habits (If I feel , I go for a long walk).
You can also use it for instructions. In this case the main clause is an imperative: If you feel tired, take a break. And you can use such as can in the main clause: If the sun is strong, plants can dry out quickly.
- Scientific facts: If you cool water to zero degrees Celsius, it turns to ice.
- General truths: If people lack exercise, their health usually gets worse.
- Habits: If I do not understand a word, I look it up.
- Instructions: If the page does not load, refresh the browser.
If or when?
In a zero , if and when mean almost the same. When people drink too little water, they feel tired is the same idea as If people drink too little water, they feel tired. Use when for something that happens every time, and if for something that happens only in some cases.
Unless means if not, and it also works in this pattern: Unless the soil is wet, the seeds do not grow. Do not add another negative after unless.
Zero or first conditional?
Learners often mix the zero and first . The difference is time. The zero conditional is always true. The first conditional is about one possible future event.
Compare: If it rains, the roads get slippery is true every time. If it rains tomorrow, we will stay at home is about one future day. Words like tomorrow, next week and this evening point to the first conditional, which uses will in the main clause.
Using it in your own answers
A zero is useful when you want to explain a cause and effect without sounding unsure. In an essay about the environment you might write: If factories release waste into rivers, fish and plants die. This sentence gives the reader a clear link in one line.
In a speaking answer about work, you can say: If I have a deadline, I usually stay late and finish it. This tells the listener about your regular behaviour, and the grammar is easy to control while you speak. You can also use it to give advice: If you want to improve your listening, watch a short video every day.
Keep the idea general. If you start to talk about one particular day, you need a different tense. Test your sentence by asking: does this happen every time? If the answer is yes, the zero conditional is the right choice.
Common mistakes
The biggest mistake is putting will or would in the if clause. We do not say If you will heat ice, it melts. After if, use the present simple. Another mistake is using the past simple for a general fact: If the price rose, people bought less is a past event, not a general rule.
A third mistake is forgetting the third person s in either clause. Say If a student works hard, he or she improves, not If a student work hard, he or she improve.
IELTS tip
In Writing Task 2, a zero is a clean way to state a general truth about your topic, such as If cities build more cycle lanes, more people cycle. In Speaking Part 3, it lets you give a general answer before you give a personal example.
Frequently asked questions
Why is it called the zero conditional?
Many course books number the first, second and third for possible and imaginary situations. General facts do not fit those three, so they are called zero.
Can I use when instead of if?
Yes. In a zero conditional, when and if mean almost the same thing. Use when if the situation happens regularly.
Can I use will in the zero conditional?
Not in the if clause. If you want to talk about a possible future event, use the first conditional, with will in the main clause.
Do I need a comma?
Use a comma after the if clause when it comes first. Do not use one when the main clause comes first.
Sources
- Swan, M. (2016). Practical English Usage (4th ed.). Oxford University Press.
- Murphy, R. (2019). English Grammar in Use (5th ed.). Cambridge University Press.