Question Word Subjects

An almost essential ingredient of a question, which differentiates it from a regular sentence is an auxiliary verb:

The Rolling Stones played lots of famous songs.
What songs did the Rolling Stones play?

In both of the examples above, the Rolling Stones are the subject. And in the question, we use the auxiliary verb did. 

But there are cases, when we don't use the auxiliary verb do in present or past simple questions, when the question word(s) is also the subject of the question: 


Who sang Sympathy for the Devil?
Which band sang "Sympathy for the Devil?

As you can see in the examples above, the question words, like who and which band, acts as subject pronouns, which substitute the unknown answer, and the auxiliary verb do is not used. The word order is the same as a regular sentence (subject before all verbs): The Rolling Stones sang Sympathy for the Devil?


This can happen in other tenses, but the auxiliary verb does not disappear:

How many bands have covered that song?

Who will be the opening band?
What song is being played on the radio?
Which songs were performed at the concert?

As you can see in the last two questions, the question word subject is common in the passive voice. And as seen in all of these examples, who, what and which, as well as how many / much joined by another noun, are the question words that can be used as subjects.

So, what is going through your mind right now?