Conditional sentences, often called ‘if clauses’, are a regular part of Lok Sewa English grammar questions. You may be asked to fill in the correct verb form, find an error or choose the sentence with the right meaning. This note explains the four main types of conditionals, mixed conditionals, words such as unless and provided, inversion without ‘if’, and the mistakes examiners test most often.
1. What is a conditional sentence?
A conditional sentence shows that one action depends on another. It has two parts: the if clause (the condition) and the main clause (the result). Example: If it rains, we will stay at home.
- The clauses can come in either order: We will stay at home if it rains.
- When the if clause comes first, put a comma after it. When the main clause comes first, no comma is needed.
- The type of conditional depends on the verb forms in the two clauses and on whether the situation is real or imaginary.
Conditionals can be divided into real conditionals (zero and first), which talk about things that are true or likely, and unreal conditionals (second and third), which talk about imaginary situations that are not true now or did not happen in the past. Knowing whether a situation is real or unreal is the first step to choosing the right verb form.
2. Zero conditional: general truths
Form: If + simple present, simple present. It is used for scientific facts, rules and things that are always true. ‘If’ can usually be replaced by when.
- If you heat ice, it melts.
- If water reaches 100 degrees Celsius at sea level, it boils.
- If you mix red and white, you get pink.
- Plants die if they do not get water.
3. First conditional: real or likely future
Form: If + simple present, will/shall/can/may + base verb (V1). It is used for a possible condition in the present or future and its likely result.
- If you study hard, you will pass the exam.
- If it rains tomorrow, the match will be cancelled.
- If he comes, I will give him the letter.
- The main clause can also be an imperative: If you see Hari, tell him to call me.
Important: do not use ‘will’ in the if clause. ‘If you will study hard, you will pass’ is wrong.
4. Second conditional: unreal or imaginary present
Form: If + simple past, would/could/might + V1. It is used for imaginary, unlikely or impossible situations in the present or future. The past form does not show past time here; it shows that the idea is unreal.
- If I had a car, I would drive to work. (I do not have a car.)
- If she knew the answer, she would tell us.
- If I won a lottery, I would build a school.
- With the verb ‘be’, use were for all persons in formal English: If I were you, I would accept the offer. If he were rich, he would help the poor.
5. Third conditional: unreal past
Form: If + past perfect (had + V3), would have / could have / might have + V3. It is used for imagined situations in the past that did not happen, often to express regret.
- If you had worked hard, you would have passed. (You did not work hard and did not pass.)
- If I had known about the meeting, I would have come.
- If she had left earlier, she would not have missed the bus.
- Wrong: If I would have known, I would have come. Right: If I had known, I would have come.
6. Summary table
| Type | If clause | Main clause | Use | Example |
|---|---|---|---|---|
| Zero | Simple present | Simple present | Facts, general truths | If you heat ice, it melts. |
| First | Simple present | will + V1 | Real, likely future | If it rains, I will stay home. |
| Second | Simple past (were) | would + V1 | Unreal present or future | If I were rich, I would travel. |
| Third | Past perfect (had + V3) | would have + V3 | Unreal past, regret | If he had run, he would have caught the bus. |
7. Mixed conditionals
Sometimes the time of the condition and the time of the result are different. These are mixed conditionals.
- Past condition, present result: If + past perfect, would + V1. If I had taken the medicine, I would be well now.
- Present condition, past result: If + simple past, would have + V3. If he were careful, he would not have made that mistake.
8. Unless, provided, in case and inversion
| Word or form | Meaning | Example |
|---|---|---|
| Unless | if … not | Unless you hurry, you will miss the bus. (= If you do not hurry) |
| Provided (that) / providing | only if | You can go provided that you finish your work. |
| As long as / so long as | only if | You may stay as long as you keep quiet. |
| In case | because something may happen | Take an umbrella in case it rains. |
| Otherwise | if not | Hurry up, otherwise you will be late. |
| Suppose / supposing | imagine that | Suppose you won a prize, what would you do? |
Since unless already means ‘if not’, do not add another ‘not’ to the same clause: ‘Unless you do not work hard, you will fail’ is wrong; say Unless you work hard, you will fail.
Inversion: in formal English ‘if’ can be dropped and the auxiliary moved to the front:
- Had I known the truth, I would have told you. (= If I had known)
- Were I in your place, I would resign. (= If I were)
- Should you need help, call me. (= If you should need help)
9. Common errors and quick checks
- No ‘will’ or ‘would’ in the if clause: If he comes (not will come); If I had (not would have) money.
- Second conditional with ‘be’ uses were: If I were a bird, I would fly.
- Third conditional needs had + V3 in the if clause and would have + V3 in the main clause.
- Match the pair: present → will; past → would; past perfect → would have.
- Unless never takes a second ‘not’ in its own clause.
| Wrong | Right | Why |
|---|---|---|
| If it will rain, we will stay home. | If it rains, we will stay home. | No ‘will’ in the if clause |
| If I was you, I would go. | If I were you, I would go. | Use ‘were’ for advice |
| If he would have come, I would have met him. | If he had come, I would have met him. | Third conditional uses ‘had + V3’ |
| If she had time, she will help. | If she had time, she would help. | Past in the if clause takes ‘would’ |
| If you mix blue and yellow, you would get green. | If you mix blue and yellow, you get green. | A fact uses the zero conditional |
| Unless you do not apologise, he will be angry. | Unless you apologise, he will be angry. | Unless already means ‘if not’ |
Tip for fill-in-the-blank questions: look first at the verb form that is already given. If the main clause has ‘would have’, the blank in the if clause must be ‘had + V3’. If the if clause has a past form, the main clause takes ‘would’. If the if clause is in the present, the main clause usually takes ‘will’ (or the present for a general truth).
📌 Key points to remember
- Zero conditional: If + present, present (facts).
- First conditional: If + present, will + V1 (likely future).
- Second conditional: If + past, would + V1 (unreal present); use ‘were’ for all persons.
- Third conditional: If + had + V3, would have + V3 (unreal past).
- Never use will or would in the if clause.
- Unless means ‘if not’; do not add another ‘not’ after unless.
- Had I known = If I had known; Were I = If I were; Should you = If you should.
- Mixed: If + had + V3, would + V1 shows a past cause with a present result.
Test yourself: Conditional Sentences (If Clauses)
20 questions on What is a conditional sentence?, Third conditional: unreal past and Common errors and quick checks.