a reason or the reason

Question

He bought the house with a big backyard. This combination tells the listener which specific house he bought.

He bought a house with a big backyard. This combination tells the listener what kind of house he bought, but not the specific house he bought.

I always thought that I can say "the house with a big backyard" whether the listener knows about the house or not.

But in the previous question regarding articles, I received an answer saying ""the" won't work if the listener does not have any information about the house before hearing about it", and said one should use "a" if the listener does not have any background information about it.

So I realized that "a" and "the" are entirely governend by whether the listener already knows it or not, not whether you are trying to specify the item or not.

I was living happily with this knowledge, until another question came into my mind.

Take a look at this conversation:

John: What did you do yesterday?

Sam (a prosecutor): I was hearing a reason a murderer killed the victim being justified.

John did not know anything about the trial, and "reason the murderer killed the victim" is new information to him. John did not know about it till Sam told him. Thus, in this case, use of indefinite article should be natural.

But it doesn't sound natural. It sounds strange.

My gut tells me that "the" should be used in that case, even though the idea is introduced for the first time, and the listener knew nothing about it.

I think the only time that "a" can be used in this sentence with "reason" is if there were more than one reason. But there was only one reason.

But why can I not use "a" in that case? Or is it actually possible?

(the dialogue is made up)

EDIT: I found a valid instance;

(2) That wasn’t a reason I left Pittsburgh, it was the reason.

From https://msu.edu/~abbottb/support.htm

Answer 1

John: What did you do yesterday?

Sam (a prosecutor): I was hearing a [or: the?] reason a murderer killed the victim being justified.

In short, the reason sounds better, because in life as we and John know it, there is usually only one reason given by, or on behalf of, a murderer. This is true, whether John has heard about this specific case, this specific trial, this specific murderer, or not. This is just the way life, and most murder trials work. (Although, Prosecutor Sam is being a little over-zealous for his cause here, because in the USA, a person is innocent until proven guilty; so a person on trial for murder, is an accused murderer, not a murder--unless he has murdered previously, but still regarding this newest trial, he is an accused murderer: still Sam could, off the record, call the person a "murderer.")

In rare cases, more than one (thus a) reason could be given, as in when people are trying to guess "the reason." But there is usually only one reason, and this one reason can include multiple facts, strands, or sub-reasons, but it can be summarized as "the reason." And this is "the reason' that Jill, the accused murderer's defense attorney is going to try to justify. Not one among many, but just this one.

If this murderer did indeed have more than one reason, then a could be used.

But it is not true that "a" and "the" are entirely governed by whether the listener already knows it or not. This is a false thesis. Read more of Abbott.

What usually governs the use of a and the is the assumption that the speaker makes about the listener. If the speaker assumes the listener can identify which referent he is talking about, then the speaker will use the. Else, he will use a. But notice even this is just a guideline. Speakers do not have to abide by this rule, and this rule does not cover the corollary, the use of a. In fact, a speaker can use a even if he knows that the listener can identify the referent. Let's go over this using the sentence a about the house.

If say to you

Our friend Jason bought the house with a big back yard.

this usually means I would expect you to be able identify which house I'm talking about. Either you are familiar with this house, because you've seen it or we've discussed it before, or something along those lines. But, usually, if I don't assume you can identify which house I'm talking about, I would use a house with a big back yard.

However, if we are limiting the discourse context to one sentence, I would probably say

Our friend Jason bought the house with the big back yard.

Notice I say both the house and the big back yard. This is because, given the discourse context of only one sentence, the house I expect you to be able to identify is identifiable because of its big back yard. This is the only characteristic of the house that distinguishes it from the other houses that Jason was considering buying. In other words, among the houses that Jason was serious about buying, only one of them had a big back yard.

If I say

Jason bought a house with a big back yard.

Taking this sentence as our only context, I would normally say it if I assumed you could not identify which house I'm talking about.

However analyzing the whys and wherefores of individual sentences shorn from any context is extremely problematic especially when taking about ten use of articles. Also important are speaker's intention, what the speaker assumes assumes, and any other context. Thus

If we are standing in front of the house that Jason bought, and it has a big back yard and I say

Well, Jason bought a house with a big back yard (just like he said he would); just look how big that back yard is!

this doesn't mean I don't expect you to be able to identify which house Jason bought. We both know which house it is: we're standing in front of it, talking about it! In this case, the noun phrase a house with a big back yard refers to a specific house, namely the one we are standing in front of and talking about. But, grammatically I am not identifying it as a definite house; for that, I would have to use the definite article.

Answer 2

I'll try to keep my answer short and sweet because this is the kind of topic you can spend hours on end talking about.

When we talk about things using the, there's typically, what I'd call, a personal history record associated with the object being talked about. And the information the record holds is unique and very specific to that particular object. Think of it as a short life story of the object. For example, if you were to say the following to one of your friends:

I bought the house with a big backyard yesterday.

while you really meant this (and that's the correct way to say it when talking about things in general):

I bought a house with a big backyard yesterday.

That the in front of house would immediately tell your friend that there was some specific information associated with the house and that would naturally elicit questions like: What? What house exactly are you talking about? I had heard you were going to buy a house, but you never told me that you had already decided which one you would buy. The one painted green or the brick one? Maybe the one on the corner? Which one exactly? There are many houses that are being sold right now.

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I was hearing a reason a murderer killed the victim being justified.

That one technically is correct (though, "I was hearing the justification for why the murderer killed a victim" is probably more natural to say for a native speaker) because he's speaking about things in general. The surrounding words are just extra fluff. They're like qualifier-words. Compare that with this:

I bought a big, red car being sold for real cheap.

big, red and being sold for real cheap are just adjectives (being sold for real cheap is not really an adjective, but bear with me) describing the kind of car you bought. They're really nothing but qualifiers that describe how large the car was, what color it was and how exactly it was being sold, but the car itself lacks a personal history to tell the world about. It's still a car in general.

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I hope now this clears things up a little bit for you. If you've still got questions, leave them down below in the comments section and I will make changes or corrections to my answer. Maybe not today though.