Moving the interrogative pro-adverb to the end of a question

Question

I am not a native speaker of English. From what I learn, 'wh' questions in English should normally be like this:

Why should we believe you?

How did she participate in the massacre?

However, recently in TV shows (from US and UK) I often hear this:

We should believe you why?

She participated in the massacre how?

Of course, the latter form is still less common than the former. From the shows, I feel that it is used more often as a quick reply to some previous statement, and/or when the speaker has some attitude, and/or when the situation is urgent.

In a sense, the latter form is easier: it does not need an auxiliary or modal verb, and it keeps the word order of a normal declarative sentence.

I wonder:

• How often do you (who live in English-speaking countries) hear the latter question form?
• Is it a new form? (maybe a tendency for English grammar to become simpler?)
• Or have these two forms co-existed for long, just serving different functions?

Answer 1

In writing, you would almost always use the (proper) first form of your questions. The second form is typically only used in informal speech, and generally accompanied by a generous dose of disbelief (sometimes even outright sarcasm), with heavy emphasis on the why/how.

I would see it as a way of intentionally beginning the sentence as if you were making a statement, and then, as though suddenly stumbling over an internal doubt, turning it into a question, encouraging others to recognise and share that same doubt.

Answer 2

Both styles of writing are perfectly acceptable. As you point out, the structure of the second set of questions matches that of the companion declarative sentences. For this reason, in spoken English, the speaker must be sure to really stress the question word to be clear.

In general, though, the style used is simply personal preference.

Note one style may make it easier to stress a certain word. For instance, it would be difficult to stress the 'you' in:

We should believe YOU why?

Rather, in that case you would phrase it:

Why should we believe YOU?

Likewise, it is probably easier to stress the 'why' in the first variation, though either would work.

Answer 3

I might decide punctuate your second examples, something like:

We should believe you — why?
She participated in the massacre — how?

because the first part of the sentence is a declaration, and the extra word changes it to a question.

One website says, "In writing dialogue, the dash is used to show breaks in thought and shifts in tone." The examples you provide seem conversational, so I think a dash could be justified.