Question word + to-infinitive

Question word + to + base form works like a short question inside a sentence: what to do = what I should do, where to go = where I should go. It often comes after know, decide, learn, remember, ask, explain, tell, show…

💡In many languages the verb comes straight after the question word, so learners often drop to (not: I don't know what say). Remember: question word + to + verb.

1. Saying you don't know or aren't sure what to do

• We're lost. We don't know which way to go.

• I'm not sure what to wear to the interview.

2. Asking for directions or instructions politely

• Excuse me, can you tell me how to get to the bus station?

• Do you know where to park around here?

3. Learning, teaching or showing how to do something — learn / teach / show + how to

• I learned how to swim when I was six.

• Can you show me how to use this machine?

4. Deciding, remembering, forgetting — decide / remember / forget + question word + to

• Have you decided where to go for your holiday?

• I always forget how to spell “necessary”.

With tell, show, teach, ask, the person comes straight after the verb, before the question word. Explain is different: explain to me how to…, or leave the person out: explain how to…

• She showed me how to fold a paper crane.

• Could you explain to me what to do next?

  not: explain me

• Nobody told us when to start.

Question word + to-infinitive means what someone should / can do, and the doer is the subject (or the person you mention). To talk about someone else or a fact, use a full clause in statement word order.

• why is not normally used this way: I don't know why I should go (not: why to go).
• Before a to-infinitive, use whether, not if: I'm not sure whether to call him.
• After learn, how is optional: learn to swim = learn how to swim.
• The pattern also follows adjectives and nouns: I'm not sure what to do. · I have no idea where to start.

• ✗I don't know what should I say.

  ✓I don't know what to say.

  Use what to + verb (or what I should say, in statement order).

• ✗Can you tell me how to getting to the station?

  ✓Can you tell me how to get to the station?

  Use the base form after to.

• ✗We didn't know where go next.

  ✓We didn't know where to go next.

  Don't drop to.

• ✗I'm not sure if to call him.

  ✓I'm not sure whether to call him.

  Before a to-infinitive, use whether, not if.

• ✗Please tell me where should I wait.

  ✓Please tell me where to wait.

  No question word order inside another sentence.

• ✗Can you explain me how to use it?

  ✓Can you explain to me how to use it?

  explain to + person.