oxford_guide_to_english_grammar

14 THE INFINITIVE
PAGE 156
125 Question word + to-infinitive
1 We can use a question word or phrase before a to-infinitive.
I just don't know what to say.
Alice wasn't sure how much to tip the porter.
Have you any idea how to open this packet?
No one told us where to meet.
This pattern expresses an indirect question about what the best action is. What to
say means 'what I should say'.
NOTE
a We cannot use why in this pattern,
b We can use whether but not if.
I was wondering whether to ring you. We'll have to decide whether to go (or not).
c After what, which, whose, how many and how much we can use a noun.
I didn't know what size to buy. The driver wasn't sure which way to go.
2 Here are some verbs that we can use before the question word:
advise someone discover know tell someone
ask (someone) discuss learn think
choose explain remember understand
consider find out show someone wonder
decide forget teach someone workout
We can also use have an idea, make up your mind and the adjectives clear, obvious
and sure.
We can also use this pattern after a preposition.
I was worried about what to wear.
There's the problem of how much luggage to take.
NOTE
To report instructions about how something should be done, we use tell/show someone how
to or teach someone (how) to.
Maureen told me how to turn on the heating. I didn't know how to do it.
Compare an indirect order.
Maureen told me to turn on the heating. She felt cold.
126 For and of with a to-infinitive
1 The pattern I'll wait for you to finish
I'll wait for you to finish your breakfast.
We've arranged for a photographer to take some photos.
We can use apply for, arrange for, ask for, call for (= demand), long for, prepare for,
wait for.
2 The pattern It's important for you to finish
It's important for you to finish the course and get a qualification.
It can be difficult for young people to buy their own home.
I'm anxious for the matter to be settled.