Verb and wh-clause

Some verbs can be followed by a clause beginning with a wh-word (how, what, when, where, which, who, or why):

• That might explain why he's unhappy.
• I couldn't decide which train to catch.
• Let's consider how we can solve the problem.

Verbs like this include arrange, calculate, check, choose, debate, determine, discover, discuss, establish, find out, forget, guess, imagine, know, learn, notice, plan, realise, remember, say, see, talk about, think (about), understand, wonder. Many of these verbs can also be followed by:
* a that-clause                                          

• I decided that I ought to leave.

* a wh-clause (except 'why') to-infinitive:                 

• Did you find out where to go?

Notice that if we add a subject in the wh-clause we don't use a ro-infinitive:

• I can't imagine what he likes about jazz.

Some verbs must have an object before the wh-clause:

• She reminded me what (I had) to do.                       
• I told Linda how to get to my house.

Other verbs like this include advise, inform, instruct, teach, warn.

The verbs ask and show often have an object before a wh-clause, but not always:

• I asked (him) how I could get to the station, and he told me.

These verbs can also be followed by object wh-word to-infinitive:

• She taught me how to play chess.                            
• I showed her where to put her coat.

We can often use the way instead of how referring to either the route or the means:

• Go back the way (that/by which) you came, (or informally Go back how you came.)
• Have you noticed the way (that/in which) he spins the ball? (or ...noticed how he spins...?)

Notice that we don't use 'the way how', (e.g. not 'Go back the way how you came'.)

Whether
We can use whether as the wh-word in a wh-clause when we want to show possible choices. Whether has a similar meaning to 'if':

• He couldn't remember whether/if he had turned the computer off.
  

Whether is commonly followed by a to-infinitive to talk about the choice between two or more possibilities. Notice that 'if is never used before a fo-infinitive:

• You have 14 days to decide whether to keep it or not. (not ...to decide if to keep it...)

Verbs that are often followed by whether to-infinitive are concerned with talking or thinking about choices, and include choose, consider, debate, decide, determine, discuss, know (in questions and negatives), wonder. Some other verbs to do with talking or thinking are not used with whether to-infinitive, including ask, conclude, explain, imagine, realise, speculate, think.

Notice the difference between these pairs of sentences. The first in each pair has a wh-clause with whether and the second has a that-clause:

• I didn't know whether the shop was shut. (= if the shop was shut or not)
• I didn't know that the shop was shut, (suggests that the shop was shut)
• They haven't decided yet whether the airport should be closed, (the w^-clause says what the choice is)
• They decided that the airport should be closed, (the that-clause says what was decided)

In rather formal contexts, particularly in writing, we can use as to with a meaning similar to 'about' or 'concerning' before a wh-clause. This is most common before whether:

• Opinion was divided as to whether the findings from the study were representative of the population as a whole, (or less formally ...divided whether...)