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Why does did require the base form of the verb, while had requires the third form of the verb when both are auxiliary verbs?

Did he like the marshmallow?

Had he liked the marshmallow?

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  • The first sentence is a preterite (simple past tense) marked by the auxiliary verb "did", which must be followed by a plain form verb, in this case "like". The second sentence is perfect tense, which consists of the auxiliary "have" followed by a past-participle verb, in this case "liked" (cf. "He had liked the marshmallow.").
    – BillJ
    Nov 23 '21 at 17:09
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    Because they are different auxiliaries with different grammar. Why should you expect them to take the same form?
    – Colin Fine
    Nov 23 '21 at 17:50
  • If all auxiliaires took the bare infinitive (or base form), you would not be able to distinguish between "I am watching", "I am watched", and "I am to watch"!
    – rjpond
    Nov 23 '21 at 18:46
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Did he like the marshmallow? Correct form, shown by green check mark

is a perfectly acceptable sentence.

Had he liked the marshmallow?

is not usually valid as an independent sentence. It looks like part of a counterfactual form:

Had he liked the marshmallow, he would have eaten more of it. Correct form, shown by green check mark

This uses the Past Perfect counterfactual to express an event that might have happened, but did not. This is a form of counterfactual conditional sometimes classified as a version of the subjunctive mood. This uses a past participle because that is how the past perfect forms work. The inversion of subject and verb marks this as a conditional form.

A non-conditional and non-counterfactual use of the past perfect might be something like

He had liked the marshmallow when he first tried it. Correct form, shown by green check mark (This may imply that he didn't like it so much later, or that he previously thought he would not like it.)

Notice that past perfect forms normally indicate a sequence of events, show one thing happening before another. These forms should not usually be used for simple, single past events with no sense of sequence or process.

"Had he liked the marshmallow?" could be a valid sentence if it was reported speech that had been backshifted. Backshifted speech is often part of a larger sentence, as in:

She asked me if he had liked the marshmallow.

If a multi-sentence speech is being reported, such a form could be a separate sentence. (See this comment) Otherwise such a form would not normally be used.

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    My son celebrated his second birthday yesterday! This morning I called my mother, who had sent a special cake. She plied me with questions about her grandson's reaction. Did the cake go over well? Had he liked the marshmallow?
    – nschneid
    Nov 23 '21 at 21:39
  • @nschneid I have added the backshifted situation to the answer. Thanks Dec 28 '21 at 16:36
  • @Bill, I have edited the answer based on the example provided by nschneid. Dec 28 '21 at 16:36

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