But all he'd tried to do (as he shouted at Uncle Vernon through the locked door of his cupboard) was jump behind the big trash cans outside the kitchen doors. Harry supposed that the wind must have caught him in mid- jump. (Harry Potter and the Sorcerer's Stone)

A great thing to do is dance the night away. (English Syntax and Argumentation, Bas Aarts)

As long as there is a to-infinitive in the subject just like the two examples, can we use a bare infinitive after the copular? (I want to know if there are some regulations in using bare infinitives: for example, the subject has to have ‘all, what, anything, etc’)

  • 2
    All I can do is shake my head and sigh.
    – Robusto
    Mar 5, 2013 at 16:08
  • @FumbleFingers Different question. At your link it's "Which is correct?", here it's "May one always?" Mar 5, 2013 at 18:03
  • @StoneyB: Since both the upvoted answers on the linked question effectively say the same as yours here, I don't really see that. As it happens, you've extended the scope somewhat by addressing forms that don't include "to do" before the copula - but OP here didn't explicitly ask about such contexts, so it's not obvious to me the question is significantly different. Mar 5, 2013 at 18:12
  • @FumbleFingers Actually, the only answer that says the same as mine is a throwaway in tchrist's initial Comment: "it’s possible that the to particle is distributing to both verbs here". Those answers might satisfy OP's first example, but not her second. Mar 5, 2013 at 18:19

1 Answer 1


The short answer is ‘No’ A marked infinitive is obligatory, as may be seen from counter-examples:

What we plan is take the train to New York.
Caesar’s objective was break the power of the Druids.

The question then becomes, Why is the bare infinitive acceptable in your two examples?

I note that in these examples, the construction with a marked infinitive is equally acceptable as without:

All he’d tried to do was to jump behind the trash cans.
A great thing to do is to dance the night away.


All he’d tried to do was jump behind the trash cans.
A great thing to do is dance the night away.

But if we invert the predication, the marked infinitive is required:

To jump behind the trash cans was all he’d tried to do.
To dance the night away is a great thing to do.

These two facts lead me to believe that what we have here is not bare infinitives but ellipses: the marker is allowed to be dropped because in each case it is preceded by a (somewhat parallel) marked infinitive, to do. This seems to be confirmed by the fact that if we delete those to dos, the resultant unmarked infinitives are no longer acceptable:

All he had tried was jump behind the trash cans.
A great thing is dance the night away.

  • But "A great thing to do is dance ..." sounds OK. (of course "... to dance..." is correct ... also.
    – Mitch
    Mar 5, 2013 at 16:52
  • @Mitch Yes, that's the construction OP cites which raises the question. Mar 5, 2013 at 16:56
  • I'm not sure what your point is. The OP wonders about leaving off the 'to', you say it's wrong, I'm pointing out that the HP example and my example don't sound wrong. Your last paragraph leads me to believe that you think it is OK though, even though you don't give any examples that it is OK.
    – Mitch
    Mar 5, 2013 at 17:04
  • 1
    @Mitch OP asks "Do these exx show that a bare infinitive is always acceptable..." I say "No" and then go on to say "The question then becomes, Why is the bare infinitive acceptable in your two examples?" ... and the answer is Because it's an ellipsis (not a bare infinitive). Mar 5, 2013 at 17:11
  • OK...I didn't get the implication of 'always' in the OP. All I saw was 'can'.
    – Mitch
    Mar 5, 2013 at 17:14

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