Which of these sentences is grammatically correct: I asked them what he did for a living, or I asked them what did he do for a living. And since both seem to be posing a question, shouldn’t there be a question mark somewhere? Let’s sort this out.
It will be best to begin by reminding ourselves of the standard word order in English for a declarative sentence, one that makes a statement of some sort, whether positive or negative. That word order, sometimes abbreviated as SVO, is subject + verb + object if there is one. If I say, for example, that my house needs a new roof, I am declaring a fact, and my reader or listener will know that because the subject of my statement, my house, precedes the verb I have attached to it, needs. If I invert the word order and employ the verb do or will as an auxiliary (as the tense requires), I transform my declaration into a question: Does my house need a new roof? Will my house need a new roof? Notice, importantly, that the tense is communicated by the auxiliary verb (does or will), not by the infinitive (need) which that auxiliary verb is helping. This holds true for all verb phrases.
Now there are two ways to ask a question, directly and indirectly. The two interrogative sentences we just created by inverting the word order and using an auxiliary verb are called direct questions. Direct questions expect a direct answer and they almost always end with a question mark. When a direct question is made part of a larger sentence, though, its confrontational attitude, so to speak, is blunted; one is then not so much asking a question, but reporting that one did ask one. These are called, appropriately enough, indirect questions. Direct questions conclude with a question mark, indirect questions do not.
If we look again now at our two original examples, we can see that each is an indirect question, because the question has become a subordinate part of a main clause, I asked them. Recognizing that, we can dispense quickly with whether either should end with a question mark—a clear no, because, as we just noted, only direct questions have the question mark. But what about the word order? The first of our examples puts its reported question in the order of a declarative statement: he, the subject + did, the verb. The second example, though, inverts this order as if it were asking a question directly: did, the auxiliary verb + he, the subject. And right there we have all the evidence we need to decide the issue in favor of the first sentence, for the rule in standard English grammar is that indirect questions are posed in the regular declarative word order of subject + verb.
Now the interesting twist here is the appearance of the verb do in the second example. Why, in order words, are there two forms of the same verb, did and do, in that sentence? For the simple reason that some verbs, like do and have and will, are employed as auxiliary verbs in addition to their acting as main verbs. The construction what did he do for a living is posing a direct question because did is acting as the auxiliary to the infinitive do, and it is only by coincidence that the same verb is being used in two different ways in the same sentence. We see the same phenomenon in a sentence like I had had enough, where the first had is the auxiliary verb and the second had is the infinitive the first had is helping to build the past perfect tense. We might wonder at the double use of the same word (particularly when they are juxtaposed), but each has its purpose and that’s justification enough.
To sum up, then. Our second example is not correct because its word order is posing a direct question in a sentence that is set up for an indirect one. And that’s a grammatical problem.
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