Art for art’s sake is the English equivalent of a French philosophy from the early 19th century, “l’art pour l’art”, that expressed a philosophy that the only value of art, and the only “real” art, is divorced from any educational, moral, politic, pornographic or any other useful function. It’s just art. I like the French, I think they might have invented, art. Such works are sometimes described as “autotelic”, from the Greek autoteles, “complete in itself”, a concept that has been expanded to embrace “inner-directed” or “self-motivated” human beings. And the art of knowing about art is knowing what to ignore.