The infinitive with and without "to"

Hello!. How are you?

Well, I found these two sentences yesterday
and, to be honest, I don?t know what is
the difference between the usage of
an infinitive with “to” and “without” to?

1.- All we have to do is SIGN a few documents…

2.- My plan is TO EXPLAIN…

Well, I would like to know if it?s possible
to use the infinitive with or without “to”
indistinctively in both sentences.
And… Could I do it as well in any sentence?

I mean…

Could I say: “All we have to do is TO SIGN…”

and… “My plan is EXPLAIN…” and be

grammatically correct?

Thanks a lot!


Actually this grammatically incorrect. Strictly speaking it should be “. . we have to do is to sign . .”, but it is accepted to drop the “to” after “to do”.
If you said “doing” it would be followed by “-ing”:
"What we are doing is signing . . ".

In this case it is essential to keep the “to”.

Sorry, dOlier, my opinion is a bit different. Both the sentences given below are grammatically correct! To after the expressions like All I did was is just optional.

  • All we have to do is sign a few documents.
  • All we have to do is to sign a few documents.


Hello! Thanks a million for your replies.

But there?s Something I still don?t understand…

1.- All we have TO DO is SIGNING a few documents…

2.- My plan is EXPLAINING…

What if I choose “to do” instead of “doing”
as you said? Would the first sentence be right,

And the second one?

Thanks again!