On Gilles Deleuze and Félix Guattari's What Is Philosophy? (1991).
How is philosophy different from science and art? What's the relationship between different philosophies? Is better pursued solo, or in a group? Deleuze described philosophy as the creation of new concepts, whereas science is about functions that map observed regularities and art is about creating percepts and affects. Just reading or writing about past philosophers is not enough; you have to actually create concepts, and to create or understand a concept requires a "plane of immanence," which is something like a set of background intuitions that is not private to a particular mind. Such a plane constitutes an image of what thought is and determines what questions will be considered legitimate, so trying to evaluate a past philosophy without grappling with the plane means you'll inevitably misunderstand the philosopher and your critiques will just talk past him or her. Likewise, if you yank a philosophical concept out of its plane and try to turn it into a proposition that you can evaluate, it's inevitably going to seem weak, like "just an opinion," because propositions are not what philosophy creates. As for a pragmatist, "truth" for Deleuze is something defined within a plane, not some transcendental standard used to judge planes or concepts.
End song: "Tolerated" by New People, the new album Might Get It Right. Read about it.