A verb form in the sentence.

[coolpro]

I have a sentence from my book "1000 Phrasal Verbs in Context":

"I never drink alcohol because all it does is BRING ON a headache".

Is the verb BRING ON in the bare-infinitive form? If yes, why would we use that?

[emsr2d2]

I have a sentence from my book "1000 Phrasal Verbs in Context":

"I never drink alcohol because all it does is BRING ON a headache".

Is the verb BRING ON in the bare-infinitive form? If yes, why would we use that?

Why would we use "bring on"? Or why would we use the bare infinitive?

We use "bring on" because it's the correct phrasal verb in this context (meaning "to cause").

We use the bare infinitive because that's what we use after "All it/he/she/etc does is..."

I don't like John. All he does is complain.
I don't eat apples. All they do is give me stomach ache.
There is a man on that street corner and all he does is sing "Jingle Bells".
School's boring. We're there for 7 hours and all we do is listen to teachers talk.

[coolpro]

emsr2d2, thanks for your quick response.

In your post, you mentioned, that we use the bare infinitive because that's what we use after "All it/he/she/etc does is..."

Is there any other situations when you're supposed to use the bare infinitive after is/was/were?

Thank you in advance.

[emsr2d2]

I have a sentence from my book "1000 Phrasal Verbs in Context":

"I never drink alcohol because all it does is BRING ON a headache".

Is the verb BRING ON in the bare-infinitive form? If yes, why would we use that?

emsr2d2, thanks for your quick response.

In your post, you mentioned, that we use the bare infinitive because that's what we use after "All it/he/she/etc does is..."

Is there any other situations when you're supposed to use the bare infinitive after is/was/were?

Thank you in advance.

All I can do is tell you what I know.
The best thing to do is shout.
There is nothing to do but sing. (Not quite the same but still the bare infinitive after "but").

Note that we wouldn't use "were" with the original examples because "is" refers to "all" or "the best thing" etc which are singular.