You might think that we’ve already summed up all English tenses in the grammatical sense with the “past,” “present,” and “future.” However, there’s one more type of tense that we ought to know about: the “conditional” or, in other words, “conditional sentences” or “if”-sentences. 

There’s a reason why we call it “conditional” because it already implies that if a particular condition is true, then a specific result happens.

Unlike the other tenses, which are described by “simple,” “continues/progressive,” “perfect,” and “perfect continues/progressive,” conditional sentences are categorized by type – four, to be exact.

Nevertheless, we’ll need the other tenses to form a complete sentence, which is structured in the “if-clause” and “main clause.” Which clause comes first and which one follows doesn’t matter since the meaning always stays the same. Only keep in mind that you have to remove the comma when you put “if-clause” after the main clause!

Type I

We use the 1st type of possible conditional sentences when we talk about a condition that is plausible to fulfill and might take place.

The if-clause is in Present Simple, whereas the main clause is in the Future Simple’s “will”-form.

• Statement: If I study early on, I’ll pass the exam.
• Negative Statement: Even if you ask him, he won’t do it. 
• Question: Will you tell him that I went back home if you see him?

💡 Type I = conditions that are possible to fulfill

Type II

Conditions that would theoretically be possible to fulfill or refer to future hypotheticals and present situations that are both unlikely or impossible to happen require the 2nd conditional type. 

The if-clause is in Past Simple, whereas the main clause consists of would/could/might + infinitive verb form. 

• Statement: If I were rich, I might buy myself a castle.
• Negative Statement: I wouldn’t do this if I were you.
• Question: Would you accept your ex-wife’s apology if she were to apologize? 

💡 Type II = conditions that are hypothetically possible to fulfill but rather unlikely to achieve or happen.

Type III 

When we talk about impossible to fulfill conditions because they’ve already expired, we use the 3rd type of conditional sentences.

The if-clause is in Past Perfect tense, whereas the main clause is formed with would/could/might + have + past participle verb form.

• Statement: If I had studied harder, I would have passed the exam.
• Negative Statement: If she hadn’t provoked him, he wouldn’t have left her.
• Question: Could he have won the competition if he hadn’t offended one of the judges?

💡 Type III = conditions that are impossible to fulfill since they’ve already expired

Type Zero

The “zero” type is used for inevitable and always true conditions, like universal truths or scientific facts. It is also the only type of conditions where we can replace the word “if” with “when.” 

The if-clause is in Past Perfect tense, whereas the main clause is formed with would/could/might + have + past participle verb form.

• Statement: When the temperature reaches zero degrees Celsius, water freezes.
• Negative Statement: You won’t get a green color if you mix red with blue.

💡 Type Zero = real conditions that are always true, like scientific facts and universal truths.