How can I explain this "Who" question simply to my student?

Question

I'm having trouble explaining to my student why you can't use "do/did" in the following sentence:

Who taught you how to play the guitar?

He thinks that it's strange there is no "do/does" in the sentence. The grammar in that sentence feels strange to him.

I said that we can't say "Who does/did taught you how to play the guitar?", but he doesn't seem to understand.

I told him that "Who did you teach play the guitar?"(he made this sentence and asked if it has the same meaning) and "Who taught you how to play the guitar?" have a different meaning, but he doesn't understand.

Can anyone help out? :(

Answer 1

Rules for making wh-questions. First locate the missing information:

1. You taught ___?

Select the correct wh-word and insert it into this space:

2. You taught who?

If, and only if, you want to move the wh- word to the front of the sentence, invert the subject and the auxiliary verb. If there is no auxiliary verb, insert the verb do:

3. Who did you teach?

In this case we didn't have an auxiliary so we inserted did. Notice that it occurs before the subject, you.

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Ok, lets try that with the Original Poster's sentence. First locate the missing information:

1. [_____] taught you to play the guitar.

Next choose the right wh-word:

2. Who taught you to play the guitar?

OK, well how about the third step. Hmmm. It doesn't look possible. We cannot move the wh-word to the front of the sentence. It's already there! For this reason we don't need to have subject-auxiliary inversion. And for that reason we don't need the word do. The question is already fully formed because the wh-word is already at the front of the sentence.

Answer 2

Taught is the past tense.
You could not use "do" (present tense) with "taught" (past tense).

You also need to look at the person. "Who taught you to play guitar" is directed at the student learning to play guitar. "Who did you teach to play guitar?" is directed to the guitar tutor.

Answer 3

The question does not require an auxiliary verb because, technically, the full version should run something like this:

Who [is the person that] taught you to play the guitar?

Answer 4

You can start from your examples:

Who(m) did you teach play the guitar?

and

Who taught you how to play the guitar?

In the first example, who, or rather whom, is an interrogative pronoun in the accusative case, which, syntactically, is a direct object. So, here, you will simply have your student translate the English who into Russian and then select from its declension paradigm the form appropriate for the accusative case; then, finally, have him / her answer the question like this: You taught Ivan to play the guitar, in which case, as in the initial question, Ivan, which refers to who(m), would also be in the accusative case.

As to the second example, have your student do the same as in the case of your first question. When, again, he / she answers the question by saying, Ivan taught you to play the guitar, your student will notice that a. Ivan once again refers to who in the question, and that b. unlike in the case of your first question, both who and Ivan are now in the nominative case because, syntactically, they are subjects.

In conclusion, on doing the replacement test:

Who taught you how to play the guitar?

turns into

Ivan taught you how to play the guitar.

As you can see, when doing this replacement test, the initial sentence, though interrogative in form, remains unchanged in its affirmative form. All that changes is who which gets replaced by Ivan.