Question

As far as I am concerned, after to be we cannot use a bare infinitive. However, I read some books and found some sentences in which bare infinitive is used after to be. E.g: What you need to do is write a well-organized essay

The above sentence is right or wrong? I suppose it should be :" what you need to do is to write...." What do you think?

Answer 1

"What you need to do is write a well-organized essay."

The main verb is 'is'. The subject is 'What you need to do'. It has a subject and a verb of its own. The subject is 'you' and its verb 'to do' is emphatic. It's inserted for emphasis.

Main verb: What you need to do is write a well-organized essay.

Take out 'need to do' and it's replaced by 'write',

Main verb: What you need to write is a well-organized essay.

Switch the words around,

Main verb: A well-organized essay is what you need to write. Main verb: A well-organized essay is what you need to do.

Answer 2

But, I think the sentence " what you need to do is to write...." is also right... I use this example often then the first one... :)