一般的な条件文「If」の使い方

Conditional sentences are common in everyday English. Indeed, "if" is one of the most common words in English. But you need to be very careful in the way you use conditionals—otherwise, you can convey the wrong meaning entirely.

Let’s start with the basics. For example: 

• If you read this blog post, you'll likely learn something new. 

Conditional sentences have two parts, known as clauses: a condition clause, usually introduced with "if"—in this case, "If you read this post..." The other part is the result clause—in this case, "...you'll likely learn something new."

Clauses can be used in either order. The condition clause can come first, in which case you follow it with a comma, or second; in this case you do NOT use a comma. So you can also say, "You'll likely learn something new if you read this blog post." 

There are four basic conditional forms. Each gives information about how likely an event is or when it happened.

Zero conditional

This type of conditional is used to describe facts.

• Water boils if you heat it to 100°C.

This zero conditional is also used for things that are generally true.

• If my son’s smiling, he’s done something naughty.

The form of the zero conditional is:

• In the condition clause:
  • if + present simple/present continuous/present perfect simple or continuous
• In the result clause:
  • present simple/present continuous

Here are more examples of the zero conditional used to express facts:

• If you mix blue and yellow paint, you get green paint.
• If you press this button, a light goes on.

Here are things the speaker believes to be true:

• If you’ve passed your exams, you’ve achieved your goals.
• If you’ve finished the job in half an hour, you haven’t done it properly.

First conditional

This type of conditional is used to describe actions or events in the future that will probably happen. For example,

• If it rains this afternoon, we can’t go to the park.

The form of this conditional is:

• In the condition clause:
  •  if + present simple/present continuous/going to
• In the result clause:
  • will, can, may + infinitive/imperative/continuous form/ going to

More examples:

• Tom won’t accept the job if they offer it to him.
• If you need me, call me.
• I’ll be working in my office if anyone requires my help.
• If the new manager increases our workload, I may quit my job.

Second conditional

This type of conditional is used in two ways. First, to describe actions or situations in the present that are not real.

• If I knew the answer, I’d tell you. (But I don’t know the answer.)

The second conditional also describes actions or events in the future that will probably not happen.

• We could retire if we won the lottery. (But I don’t expect that we will win the lottery.)

The form of this conditional is:

• In the condition clause:
  • if + past simple/past continuous
• In the result clause:
  • would, could, might + infinitive/continuous form

Here are more examples of the second conditional for actions or situations in the present that are not real:

• If I were in Bali, I’d be lying on the beach right now. (But I’m not in Bali.)
• I could be playing you my favourite death metal tracks if my parents weren’t sleeping right now. (But my parents are sleeping right now.)

Here are more examples of the second conditional for actions or events in the future that will probably not happen.

• If I was abducted by aliens, I’d try to communicate with them. (But I don’t think that will ever happen.)
• If you were waiting at a bus stop and Brad Pitt walked past, what would you say to him? (But I think such a situation is highly unlikely.)

Third conditional

This type of conditional is used to describe impossible actions or situations in the past. The speaker is imagining what would have happened if things had been different. For example,

• Nancy would have arrived at the interview on time if she hadn’t lost her car keys.

The form of this conditional is:

• In the condition clause:
  • if + past perfect simple/continuous
• In the result clause:
  • would, could, might + perfect infinitive/continuous form

Here are more examples of the third conditional:

• If you had been listening to the teacher, you would have understood what the word means. (But you weren't listening to the teacher so you didn't understand what the word means)
• If I hadn’t studied Sociology at university, I might have chosen History instead. (But I studied Sociology so I didn't study History)
• We could have arrived at our destination sooner if Mary hadn’t insisted on stopping for lunch. (But Mary insisted on stopping for lunch so we didn't arrive sooner)
• I would have been waiting at the railway station for ages if my brother hadn’t come to pick me up. (But my brother came to pick me up so I didn't have to wait at the station for ages)

I hope this has helped to clarify the forms and uses of the common conditional forms. To learn more about the other types of conditionals, have a look at Mixed conditionals and Alternatives to 'if' in conditional sentences.