Thesis Antithesis Synthesis
Often attributed to the philosophers Hegel or Marx, these terms have been used to describe the development of reasoning about evidence. They sometimes even occur in historically documented events, but they probably are best thought of as a convenient mental model for styles of thought. That is, they help us decide how to position ourselves in the flow of scholarly discourse about our topic. It's always hard to find a "starting place" for real knowledge because it always builds upon old knowledge, either making it better or demolishing it or some compromise in betweeen. But the pattern of the discourse flow, a repeating conversation, will become familiar to you. It usually goes like this.
1) Are we beginning something new? (Nobody has ever thought of interpreting Casablanca as a film noir.)
In that case, we position our ideas as a thesis. (The similarities in this evidence from films noir and from Casablanca suggests that Casablanca is a film noir.)
2) Are we responding to something a previous thesis asserts? (X has argued that Casablanca is a film noir.)
In that case, we position our ideas as an antithesis to a previous thesis. (X suggests Casablanca is a film noir, but this is unlikely because films noir typically end with the hero's destruction and the triumph of evil's power.)
3) Are we responding to the existence of a debate between a thesis and its antithesis, or to a series of theses? (X says Casablanca is a film noir and Y says it is not.)
In that case, we position our ideas as a synthesis of the thesis-antithesis dyad or the series of theses.
(X has recently argued that, based upon comparison of evidence from other films noir and from Casablanca, that Casablanca ought to be viewed as a film noir. Y challenged X's argument by drawing our attention to evidence in Casablanca and in films noir that suggests Casablanca should not be viewed as a film noir. Z recently has proposed a subgenre of film noir which he calls "ironic film noir," based on evidence from films X and Y do not consider, like Repo Man (1984) and Diva (1981), films in which the triumph of evil and destruction of the hero are thwarted at the last moment by supernatural or extremely unlikely interventions in a world that remains deeply corrupt. If we look at X's and Y's evidence in the light of Z's reasoning, we probably should conclude that Casablanca is best understood as an ironic film noir, but with a comic rather than satiric attitude toward its characters and their dilemma.)
Don't make the mistake of assuming that all theses have to be positive and all antitheses have to be negative. Note that the thesis might easily have begun arguing that Casablanca was not film noir if X had begun by analyzing the roles played by Bogart, Greenstreet, and Lorre in previous films noir and argued that the differences between their characters and the plots of those movies and those of Casablanca meant that Casablanca was meant to be viewed as a rebellion against film noir to promote positive views of society in a time of war. In that case, Y's antithesis might well have looked for similarities between those same characters and plots to argue that Casablanca was a failed film noir, a genre hijacked by the Hollywood studios from the auteur directors in a truly "corrupt city" that was the whole world, now that war had become a global norm.
Syntheses also do not always arise from the happy discovery of the solution in someone else's published reasoning. Sometimes we have to come up with the synthesizing position ourselves. Had Z's article not existed, the synthesis might have agreed with X that Casablanca was similar to films noir but also might have agreed with Y that it was not similar enough to films noir for twentieth-century audiences to view it that way. Then the synthesis might have offered its own way to view the movie as playing with film noir conventions while it subconsciously flirts with some other, culturally taboo notions (e.g., the tragedy of a misunderstood, sympathetic African-American musician who was treated like a servant and betrayed to the criminal underworld and the Nazis [Sam's the mediator of Rick and Ilsa's entire romance, but who does he wind up with? Ferrarri, the creep! And won't the Nazis eventually figure out his boss had something to do with Strasser's murder?], or homoerotic "bromance"? ["Rickie" and "Louis" do walk off into the future together, eh?]).