Leo Tolstoy dedicated an entire book to the definition of art.
What is and what isn’t art.

He analysed existing definitions and gave reasons why he believed that these were wrong definitions, and, of course, why his definition was better.

How the heck did he know what is and what isn’t art?
Who gave him the authority to establish one true definition of it?

Of course, he is not alone. More people did that.

Does it matter what the right definition of art is? Who is / was right and who isn't / wasn’t…