Sentences with "not"

Yes, they agree.

I concur.

Thank you.

Though "but" instead of your suggested "so" is okay in my opinion. Bryan tells Cathy he thinks about his thing..."but they are not the same then" as Cathy had told him before.

I explained my reasoning. With the limited context, my point stands. Perhaps you could offer more context so that this can be cleared up.

Bryan: Is that an old photo of your friend?
Cathy: No, I don't think so.
Bryan: Okay, I always need to think about that person on the picture, who I thought was your friend. But they are not the same then.

So?

Bryan: But they are not the same then.
Cathy: No they aren't.

The "no" confuses me. So I ask myself what Cathy want's to say with her answer:
a) That's wrong. In my opinion they are the same.
b) I agree, They are not the same.
______________________________________________

The answer to your question is that Cathy's answer indicates that she agrees with Bryan.

As far as using the word so instead of but, I will try to explain. Using the word but to begin a sentence in response to another person's statement usually indicates a dissent from the position of the previous speaker. Since Bryan is speaking with Cathy, and Cathy is in agreement with Bryan, the word but doesn't really work. The word so is the better choice.
______________________________________________

Bryan: Is that an old photo of your friend?
Cathy: No, I don't think so.
Bryan: Okay, I always need to think about that person on the picture, who I thought was your friend. But they are not the same then.
______________________________________________

Here you offer more context, but you have reversed the order in which the statements are made. Are you aware of that?

They aren't in reversed order?

Bryan: Is that an old photo of your friend?
Cathy: No, I don't think so.
Bryan: Okay, I always need to think about that person on the picture, who I thought was your friend. But they are not the same then.
Cathy: No they aren't


It is like in my first post. I just left out Cathy's last answer. And I can't get the point why "but" does not fit here.

If Cathy were Brians' biological sibling, would it matter?

What has that to do with it?

Apologies for saying that you reversed the order of statements.

However, in your first post, you didn't leave out Cathy's last answer. You left out her first answer. You also left out Bryan's first statement. You also left out most of Bryan's second sentence. In the more complete version of the conversation, the word but fits.

Okay Sorry, and thank you for your answer.
If you read the complete conversation both still agree that the person they are talking about is not the same, correct?
Or does Cathy correct her statement in the end?

Bryan: Is that an old photo of your friend?
Cathy: No, I don't think so.
Bryan: Okay, I always need to think about that person on the picture, who I thought was your friend. But they are not the same then.
Cathy: No they aren't

It has everthing to do with it.
Are you not following?
Bryan's role is now being overlooked, because - Suddenly it's redundant?
Not cool.

Correct.

I would like to add that, at this point, if I ever see Bryan or Cathy on the street after today . . . Well, let's just say that it will be better for them if I don't.

Okay, then thank you all.

But does somebody guess what Mark Nobles answers tell?:
"If Cathy were Brians' biological sibling, would it matter?"
and
"It has everthing to do with it.
Are you not following?
Bryan's role is now being overlooked, because - Suddenly it's redundant?
Not cool. "


Are these just meant to be funny or do these have a serious meaning?

Sorry we are out of sync Dylan - Was meant as an additional interest.
NOT IMPORTANT But worth considering if nothing better to do.

Okay, thank you, I was just irritated what you want to tell me with it. I am Sorry too. But to get the meaning is realy important for my English learning.

But you also still think (looking at the whole Conversation), that Cathys last statement (No they aren't) is meant as "I agree, they are not the same", correct?

Bryan: Is that an old photo of your friend?
Cathy: No, I don't think so.
Bryan: Okay, I always need to think about that person on the picture, who I thought was your friend. But they are not the same then.
Cathy: No they aren't

Agreed.
They disagree.

Sorry if I failed to take your language-skills into consideration, Dylan - But your english is very good, fella.

I do not understand what you mean with agree and disagree? Glennn told me they agree that they both think they are not the same, so where do they disagree?