You anticipated the wrong answer to your very first question. Here's how it should go.
Paul: "One thing exists for sure: Thought".
Harv: "How do you know?"
Paul: That's an interesting question but an unimportant one. I'll answer your question but then I'll pose the important one:
The way in which I know is inexplicable. In other words, I am unable to explain how I know thought exists. As good as I am with language, I am unable to compose a paragraph that satisfactorily explains to me how I know that thoughts exist. But even if I could accomplish that and come up with an explanation I was happy with, I am convinced that you would misunderstand my explanation.
Now, the important question is not "How do you know", but "Do you agree with me, Harv?"
You must have an opinion on the question. It is a simple binary question to you, Harv: Do you believe that thought exists, or not? Yes or no.
If you say, "Yes", it could very well be that the way in which you know, and the way in which I know, might be very different. Since neither of us can explain our methods of that discovery to the other, it is rather pointless to compare methods.
The important thing is that we agree, and as a result, we have a truth that we both acknowledge and which we both can use as a basis to build up further knowledge -- or at least we can try.
Now, if you say, "No", that is, you deny that thought exists, you are telling me that you don't think. Or, that you have no thoughts. What should I conclude from that answer? That you are an automaton? Someone has written a good program which passed the Turing test and turned it loose on this forum using the name 'Harv'?
Come to think about it, re-reading your script, I see that I was doing all the talking and you seemed to be in a loop! I wrote a program like that once or twice also.
Hmmm. I guess anything's possible. It could also be that solipsism is true after all!