Both Carnap and Schlick were logical positivists and members of the Vienna Circle who believed that the only meaningful statements were those that could be empirically verified. Statements that could not be verified by sense data were said to be "nonsense".

Quine was a 20th century analytic philosopher who was highly critical of Logical Positivism. Not too much about his philosophy relates to the comic. You can see more about him in the comic 28, and the notes there.

Nelson Goodman was an American analytic philosopher, perhaps most famous for his essay The New Riddle of Induction, which questions our ability to distinguish between lawlike generalizations (i.e. gravity - masses always attract) and accidental ones (all ravens are black, but we might find white ones one day). See more on the notes on comic 2.

William James was an American psychologist and philosopher, and one of the chief figures in the philosophical school of pragmatism. He believed that knowledge claims only had meaning insofar as they were useful to the believer. So the truth of anything is dependent only on its use.

Camus was sexy as fuck.