Conditionals in English are used to express relationships between ideas, either real or hypothetical/imaginary.

The main conditionals are numbered 0–3, with two additional forms used to express relationships between ideas in mixed time frames. Additionally, there are related conditional forms used to express wishes and regrets. Advanced variations of all these forms are used to express formality or sophistication.

Verb Tense Shift

There is a shift of tenses in verbs when forming conditional statements. The past simple is used to express present conditionals. The past perfect is used to express past conditionals. This pattern is used in conditionals (2), (3), mixed time frames, wishes, regrets, irritation/criticism, and preferences.

• Condition is TRUE in the present or future: past simple
  e.g. If I were you, I would consider my options
  form: past simple | would/could/might + infinitive without ‘to’
• Condition was TRUE in the past: past perfect
  e.g. If it had been me, I would have considered my options.
  form: past perfect | would/could/might + have + past participle

Conditionals 0–3

0. Real situations, general truths:
   form: if/when + present tense | present tense
   e.g. If we work, we eat.
   e.g. When it’s sunny outside, I feel happy.
1. A possible condition and its probable result:
   if + present tense | future (will)
   e.g. If you don’t tell her how you feel, you’ll lose her forever.
2. A hypothetical present condition and its probable result:
   if + past tense | would/could/might + infinitive without “to”
   e.g. If I were you, I would demand an apology.
3. An imaginary past condition and its probable result in the past
   if + past perfect | would/could/might + have + past participle
   e.g. If that had happened to me, I would have been really angry.

Mixed Time Frames

Mixed time frames are used to express relationships when a past condition has a present impact or result, or when a present condition has a past cause or result.

1. An unreal past condition and its effect or result in the present
   form: if + past perfect | would/could/might + infinitive without “to”
   e.g. If he hadn’t been more careful, he would be dead by now.
2. A present or continuing condition and its effect or result in the past
   form: if + simple past | would/could/should/might + have + past participle
   e.g. If he passed the test, he would have been admitted to medical school.

Wishes & Regrets

Wishes and regrets are expressed using a conditional form, the second clause is optional. Variations on these forms are used to express irritation or criticism in the moment and preferences.

1. Wishes: wish
   1. Present wishes are expressed using the past simple.
      form: wish + past simple + infinitive
      e.g. I wish I were taller.
   2. Past wishes are expressed using the past perfect.
      form: wish + past perfect + infinitive
      e.g. I wish I had filed my taxes on time so I wouldn’t have to pay a penalty.
2. Regrets: if only
   1. Present regrets are expressed using past simple.
      form: if only + past simple + infinitive
      e.g. If only you were better at math, you might get admitted to a better university.
   2. Past regrets are expressed using the past perfect.
      form: if only + past perfect + infinitive
      e.g. If only I had known how lucrative Apple stock would become back in the 1980s!