Gould and his insanity

Gould is insane. Was he always insane? Maybe. He is definitely insane at the time of writing this book and because of that I believe the entire story to be fictitious. This of course goes without saying, for we already know the book, Gould's Book of Fish written by Flanagan, to be a work of fiction. But I believe it goes further than that. I do not believe that most of the characters, if any, actually exist. They may be a figment of Gould's imagination they may be a figment of Hammet's imagination, who knows. I do know that I find it quite odd that Gould is able to switch seamlessly into the 3rd person or the 1st person omniscient. And for those that argue that he is simply speculating what the other characters are thinking or that he read about it in some letters later, there are other instances where he specifically says that he found out later from reading letters or from hearing about it from a friend of a friend and these instances are noticeably different than the times when he actually knows what the other characters are feeling/thinking. As for how he is able to know the thoughts and feelings of these other characters, I have already explained that. They do not exist except in his mind alone and because of that they are simply parts of himself. So of course he is going to know what they think and feel, because he is them and they are him. Whether this is the mind of Gould that we're talking about or the mind of Hammet, I still do not know.