Conditional sentences

A conditional sentence has two parts: the if-clause gives the condition, the result clause says what happens. The tenses you choose depend on whether the situation is real / possible or only imagined.

This lesson focuses on the zero and first conditionals, with a short preview of the second at the end. The second and third conditionals have their own lessons: “Second conditional”, “Third conditional”.

The two parts can change places. When the if-clause comes first, use a comma; when it comes second, you don't need one.

• If you're tired, we'll go home.

  if-clause first — comma

• We'll go home if you're tired.

  if-clause second — no comma

Use the present simple in both parts for things that are always true: natural laws, habits, “every time this happens, that happens”. Here if means almost the same as when (whenever).

• If you heat ice, it melts.

• If I drink coffee after 4 p.m., I can't sleep.

• Plants die if they don't get enough light.

• If you mix red and yellow, you get orange.

Use it for something that can really happen in the future. The if-clause uses the present simple (even though the meaning is future); the result clause uses will / won't + base verb.

• If it rains tomorrow, we'll stay at home.

• If you don't hurry, you'll miss the bus.

• What will you do if you don't get the job?

• If Nam calls, I'll tell him you're out.

The result clause doesn't have to use will. It can also be an imperative, can, may/might, should, be going to…

• If you see Lan, tell her to call me.

  imperative

• If we leave now, we might catch the 8:15 train.

  might

• If you feel dizzy, you should sit down.

  should

• If the weather is nice, we're going to have a picnic.

  be going to

💡Many learners put a future form in both parts or add a linking word before the result. In English the if-clause stays in the present simple, and the result clause needs no extra word — “then” is possible but not common, and “so” is wrong here.

when = you are sure it will happen; if = it may or may not happen (see also the lesson “Future time clauses”). unless = if … not; the verb after unless is positive.

• I'll call you when I get home.

  I'm sure I'll get home

• I'll call you if I need help.

  I may or may not need help

• Unless you leave now, you'll be late.

  = If you don't leave now

• We'll eat outside unless it rains.

Besides unless, there are in case, as long as, provided that… — see the lesson “Unless / in case / as long as”.

The second conditional (if + past simple, would + base verb) is for imagined situations — unreal or unlikely. The past tense here does not mean past time; it means “far from reality”. For the same situation, choose the first conditional if you think it can happen, and the second if you think it probably won't.

• If I find a cheap ticket, I'll fly home for Tet.

  first — quite possible

• If I won the lottery, I'd buy a house for my parents.

  second — just imagining

• If I see Hung tomorrow, I'll tell him.

  I may well see him

• If I saw Hung, I'd tell him.

  I probably won't see him

• If I were you, I'd take the job.

  giving advice

• In the second conditional the if-clause uses the past simple, not would: If I had more time… (not: If I would have…).
• With a past if-clause, the result clause uses would (or could / might), not will.
• If I were you is a fixed phrase for advice; in everyday speech people also say “if I was”, but “were” is the standard form.

💡A quick test: “Could this really happen?” Yes → present + will. Only imagining → past + would. Don't mix them: not “If I had…, I will…”.

• ✗If it will rain, we'll cancel the picnic.

  ✓If it rains, we'll cancel the picnic.

  In a first conditional the if-clause uses the present simple, not will.

• ✗If she call me, I'll tell her the news.

  ✓If she calls me, I'll tell her the news.

  It's the present simple, so he/she/it needs -s.

• ✗Unless you don't hurry, you'll be late.

  ✓Unless you hurry, you'll be late.

  Unless already means “if not”, so the verb after it is positive.

• ✗If it rains, so we will stay at home.

  ✓If it rains, we will stay at home.

  Don't use so to join the two parts; no linking word is needed.

• ✗If I would have more time, I would travel.

  ✓If I had more time, I would travel.

  The second conditional doesn't use would in the if-clause.

• ✗If I had a car, I will drive you.

  ✓If I had a car, I would drive you.

  A past (imagined) if-clause goes with would, not will.