The first culture: art
The second culture: science
The third culture: "scientists who communicate directly with the general public"
The fourth culture: "one that seeks to discover relationships between the humanities and the sciences."
"This fourth culture. . .will ignore arbitrary intellectual boundaries, seeking instead to blur the lines that separate. It will freely transplant knowledge between the sciences and the humanities, and will focus on connecting the reductionist fact to our actual experience. It will take a pragmatic view of the truth, and it will judge truth not by its origins but in terms of its usefulness. What does this novel or experiment or poem or protein teach us about ourselves? How does it help up to understand who we are? What long-standing problem has it solved?"
-Jonah Lehrer in Proust Was a Neuroscientist