Should I use the past tense with did? For example, I was to say:
The important question is: Did they knew what it means or not?
Or should I say:
The important question is: Did they know what it means or not?
In other words: Should I use past tense with did?
I looked at this:
Explanation of "did was [verb]" structure
but it didn't really answer my question.
Best Answer
Generally speaking, only the first verb in each clause is finite:
Here, know is the finite verb. It changes form to agree with the subject (I know, she knows) and to indicate tense (They know, they knew).
To turn this into a question, we need to apply Subject-Auxiliary Inversion. But to do that, we need an auxiliary, so we add the dummy auxiliary do:
Now do is the finite verb. It changes form to agree with the subject (I do, she does) and to indicate tense (They do, they did). The second verb, know, is non-finite and does not change form.
*Did they knew has two finite verbs and is ungrammatical.