What you can do is just enjoy yourself.

[kachibibb]

Say, I am writing to promote a vacation package. And I want to write this sentence:

What you can do here is (to) just enjoy yourself.

I remember someone told me before, in the above kind of situation, "to" is optional or omitted? Is it true? But I forget the reason.

 

[emsr2d2]

It can be omitted. In fact, that sentence is better without "to".

 

[kachibibb]

So both with "to" and without "to" are okay.

What is the grammatical reason for the omission?

 

[Tdol]

What's the subject of the sentence?