Q: Why don’t we go another way?
A: To save money.
There isn't anything ungrammatical about either sentence here. But, the social interaction between the two speakers seems to be wrong. There is a problem with the pragmatics.
It's important to note, though, this might just be because we haven't heard the rest of the conversation. This could be a perfectly normal exchange. We'll look at that a bit later.
Here's why the response above is strange. Grammatically, we can identify different types of clause. The Cambridge Grammar of the English Language (Huddleston & Pullum, 2002, p. 853) identifies five main types of clause:
- Declarative: You are quiet
- Closed interrogative: Are you quiet?
- Open interrogative: When are you quiet?
- Exclamative: How quiet you are!
- Imperative: Be quiet
These different types of clause have different grammatical properties. Notice, for example, that in the interrogative clauses there is subject auxiliary inversion are you instead of you are. Also with the imperative, we see a grammatical sentence that has no subject, unlike the in the other examples. The exclamative has a wh- word fronted to the beginning of the clause, but unlike the interrogative clauses, there is no subject auxiliary inversion. We see you are, not are you.
Now, we tend to associate these different types of clause with specific types of communicative acts. So we associate declarative clauses with people making statements. We associate interrogatives with questions, in particular questions asking for information. We associate exclamatives with exclamations and we associate imperative clauses with people giving directives (telling people what to do).
However, we don't always use imperatives when we want to make a directive. For example look at the following sentence:
- You must be there by 5pm.
The sentence above uses a declarative clause. However, it is being used as a directive. The speaker is telling the listener what to do. We can also use declarative clauses to make questions:
- You gave it to her?
A: Lady Gaga fainted!
B: Lady Gaga did what?
The questions in the examples above are declarative clauses, not interrogative ones (notice that there is no subject auxiliary inversion in the Lady Gaga question, even though it uses the interrogative word what).
In the original Poster's example, we see an interrogative clause:
- Why don't we go another way?
However, negative interrogative clauses using why are usually not questions they are usually directives. They are usually suggestions. The Original Poster's interrogative would normally be interpreted similarly to:
Because this is not a question, because this is really a suggestion, the response is wrong:
To save money.
We understand this phrase as an infinitive of purpose. It tells us why we did or did not do something. But the speaker is not (in the normal reading) asking for information. They do not want to know why we do something. They are making a suggestion. So a correct response to Original Poster's first sentence is something like:
This is a way of agreeing to the suggestion that we go a different way.
Sometimes a sentence can have more than one meaning. If we do not have a clear context for the sentence, we will just give it the most likely reading. With negative why-interrogatives, we will normally read the sentence as a suggestion, unless there is some reason to believe that the action described did happen, does already happen, or will definitely happen. If we assume that the action we are reading about does happen, or will (continue to) happen, we are likely to read the sentence as an information question:
- A It's always really slow this way. I don't mind it being slow, I prefer it. But I was wondering, why do we go this way? Why don't we go the other way?
If we assume that the speaker expects to continue going this way, we won't interpret the interrogatives in these examples as suggestions. They are questions seeking information. In this situation the correct response would be:
The reason that we decide that the response in the Original Poster's example is bad, is that without any other information, we automatically assume that the first sentence is a suggestion. Having already interpreted it as a suggestion, the response seems inappropriate. We have seen though, that in reality it is not necessarily wrong.
The purpose of this question in the textbook is to see if students understand this method of making suggestions. It is testing their interpretation of Why don't we-sentences.
When ambiguous sentences like this lead us to one particular interpretation even though they (might) have another meaning in this context, we sometimes call them "garden path" sentences. We could argue that the answer to the Original Poster's example was correct. Because we did not have any context, the first sentence was a garden path sentence. We are just misunderstanding the question. However, if you want to pass an English test, it is important that you can recognise interrogatives used as suggestions.
Garden path sentences are often used in jokes. Here is one of my favourites:
There were two goldfish in a tank. One of them turned to the other and said: "How do you drive this thing?"
Notice that this feature of why-interrogatives is not shared by negative interrogative clauses which use different wh- words. For example, consider:
- Who didn't he tell?
- For what reason do we not go another way?
Neither of these would be interpreted as a suggestion. Also notice that to save money is a good answer to the second question here.