I have noticed this error in non-native speakers more and more recently**, but I don't know how to explain it, i.e., I don't know what this phenomenon is called nor what the rule is. An example:

Does this work?


Yes, that works.

Note the change from work to works. I think generally this happens when we go from declarative to interrogative but I'm not sure. It also doesn't seem to happen to the first person:

Do I run every morning? Yes, I run every morning.

Does he run every morning? Yes, he runs every morning.

**The error is when people do not do this, e.g., "Yes, that work."

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    It's not an error. In interrogative clauses the dummy auxiliary verb "do" requires an infinitival complement. Thus, in your example "does" requires the infinitive verb "work". the same applies to "Do I run every morning? / Does he run every morning?" where dummy "do" requires the infinitive "run". Dummy "do" is of course tensed, and it's not possible to have two tensed verbs in the same verb phrase. – BillJ Jul 2 at 10:06
  • Thanks @BillJ - I edited the question to make it more clear that the error I was referencing was when people do not do this and I correct it, but can't give an explanation as to why. Only "that's just how it is", which feels grossly inadequate. – Derek Allums Jul 2 at 11:48
  • @PhilSweet Title corrected - thanks. – Derek Allums Jul 2 at 11:49
  • There's no change in conjugation. "Do" is dummy auxiliary verb, while "work" and "run" are infinitival verbs. Subject-auxiliary inversion is a rule. – BillJ Jul 2 at 11:58
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    Do-support is usually mandatory with normal interrogatives, but only used for stress in declaratives. "That does work." And the infinitive (not a different agreement, though it may look as if it is) is again necessary. – Edwin Ashworth Jul 2 at 12:01

[1] Does this work?

[2] Yes, that works.

In a clause like [1] the dummy auxiliary verb "do" is used to form the interrogative, and it's this verb that is marked for tense and person ("do/does/did"). It's not possible to have two tensed verbs in the same verb phrase, so the complement of dummy "do" must be the unchanging plain (infinitive) verb form, in this case "work".

Thus, in [1] the dummy auxiliary "does" marks the present tense, and "work" is the required plain form.

[2] is not an interrogative, so dummy "do" is not required. Here the tense is marked on the lexical verb; in this case "works" is present tense.

The same grammatical rule applies to the interrogative in your other examples, where dummy auxiliary "do / does" is followed by the plain form "run".

Note: the placing of an auxiliary verb like "do" before the subject in interrogatives is called 'subject-auxiliary inversion'.

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I don't know what this phenomenon is called nor what the rule is.

It is called "question formation in English"

It is absolutely standard. When you have a 'helper' verb, the helper verb is conjugated and the main verb keeps its infinitive form.

Here are the rules:

Question formation in English is different from the formation of other sentences in two main ways. https://www.englishhints.com/question-formation.html

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