What I can't do is... find an answer to this problem!

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Hi there,
Can anyone help me with an explanation for why the verb form following the 'What' statement here is the plain form of the verb and cannot be -ing or to+infinitive?

What we want to do is play with ourselves all day long.
What we need to do is fill ourselves with ice cream on hot summer's days.
What we mustn't do is panic when our students ask us tricky questions like this!

Thanks! Might grateful for your help!

AlpheccaStars · Accepted Answer

When I get a sticky question, I simplify it down to its bare essentials. The simplest sentence is:

This (subject) is (verb) ice cream (predicate noun)..
Expanding to approach your example:

What we want is ice cream
"What we want" is a clause used as a noun. It is the subject of the verb "is"
Next step:

What we want is (to eat ice cream). - "to eat ice cream" is the infinitive phrase used as the predicate noun. "ice cream" is the direct object of "eat". For clarity, I can also write:

This is what we want to do.
what we want to do is the predicate noun, following the verb "is. "to do" is an infinitive phrase, direct object of the verb want.
Next step:

What we want to do is to play.
In this case, "What we want to do" is the subject. "is" is the verb, and "to play" is the infinitive predicate noun.
Next, we realize that frequently in chains of verbs the infinitive marker "to" is omitted.
What we want to do is play.
Now we are almost there. We only have to tack on the adverb phrase "all day long" and the prepositional phrase "with ourselves"

Avangi · Answer

Anonymouswhy . . . . here is the plain form of the verb and cannot be -ing or to+infinitive?

The interesting thing about it is, the plain form of the verb is the infinitive, without its marker ("to"). The question remains, why do we drop the marker? Because we have another infinitive right in front of it with the "to" intact?? ("to do") Perhaps. (see previous post, "chains of verbs").

So "to do" is really the culprit, not the what clause. If we toss it out, you may then have your way, and choose -ing or to+infinitive.

What we like is playing with ourselves all day long.

What we need is to fill ourselves with ice cream on hot summer's days.

What we must avoid is panicking when our students ask us tricky questions like this!

What I can't do is... find an answer to this problem!

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