This page is part of a publication called Number One ESL Discussion Book & Reference Guide.
Conditionals are sentences that express the relationship between an action or event and its result or outcome, in the form of “if X, then Y”. There are several types of conditionals, including zero conditionals, first conditionals, second conditionals, third conditionals, and mixed conditionals, which vary depending on the time frame and the level of possibility of the conditions and results. Conditionals are used to talk about things that might or might not happen in the future, or to talk about things that would have happened differently in the past.
Zero Conditional
The zero conditional is a type of conditional sentence that expresses a general truth or a scientific fact, and is used to describe a situation where the outcome is always the same given the same conditions. The zero conditional is formed with the present simple tense in both the “if” clause and the main clause.
Examples of zero conditional sentences:
Statement: If water reaches 100°C, it boils.
Yes/No Q&A: If water reaches 100°C, does it boil? (Yes, it does.)
Information Q&A: What happens if water reaches 100°C? (It boils.)
First Conditional
The first conditional is a type of conditional sentence that expresses a possible future situation and its likely result. It is used to talk about something that might happen in the future, and the action that will be taken as a result. The first conditional is formed with the present simple tense in the “if” clause, and the future simple or “will” in the main clause.
Examples of first conditional sentences:
Statement: If it rains, I will stay at home.
Yes/No Q&A: If it rains, will you stay at home? (Yes, I will.)
Information Q&A: What will you do if it rains? (I will stay at home.)
Second Conditional
The second conditional is a type of conditional sentence that expresses a hypothetical or contrary-to-fact condition in the present or future, and its hypothetical result. It is used to talk about something that is unlikely to happen or is impossible in the present or future. The second conditional is formed with the simple past tense in the “if” clause, and the conditional “would” or “could” in the main clause.
Examples of second conditional sentences:
Statement: If I won the lottery, I would quit my job.
Yes/No Q&A: If you won the lottery, would you quit your job? (Yes, I would.)
Information Q&A: What would you do if you won the lottery? (I would quit my job.)
Third Conditional
The third conditional is a type of conditional sentence that expresses a hypothetical condition in the past and its hypothetical result, in order to talk about a past situation that did not happen. It is used to talk about something that did not occur in the past and its possible result. The third conditional is formed with the past perfect tense in the “if” clause, and the past perfect conditional “would have” in the main clause.
Examples of third conditional sentences:
Statement: If I had studied harder, I would have passed the exam.
Yes/No Q&A: If you had studied harder, would you have passed the exam? (Yes, I think I would have.)
Information Q&A: What would have happened if you had studied harder? (I think I would have passed the exam.)
Mixed Conditionals
There are two types of mixed conditional sentences: Mixed third/second conditional and mixed second/third conditional. These mixed conditionals combine elements of the second and third conditional forms to express hypothetical conditions in the past and their possible consequences in the present (mixed third/second conditional), or hypothetical conditions in the present and their possible consequences in the past (mixed second/third conditional).
Mixed third/second conditional:
If + Past Perfect, Present Conditional (would/wouldn’t + base form of the verb).
Example: If I had studied harder in school, I would have a better job now.
More examples of mixed third/second conditional:
Statement: If I had known about the traffic, I wouldn’t be late.
Yes/No Q&A: If you had known about the traffic, would you still be late? (No, I wouldn’t be.)
Information Q&A: Where would you be if you had known about the traffic? (I would already be at work.)
Mixed second/third conditional:
If + Simple Past Tense, Perfect Conditional (would have /wouldn’t have + Past Participle).
Example: If I spoke French, I would have understood them.
More examples of mixed second/third conditional:
Statement: If she wanted to learn how to cook, she would have taken cooking classes.
Yes/No Q&A: If she wanted to learn how to cook, would she have taken cooking classes? (Yes, I think she would have.)
Information Q&A: What would she have done if she wanted to learn how to cook? (I think she would have taken cooking classes.)