In critical theory, a binary opposition (also binary system) is a pair of terms or concepts that are theoretical opposites. In structuralism, a binary opposition is seen as a fundamental organizer of human philosophy, culture, and language.
In Ferdinand de Saussure’s Course in General Linguistics (written by Saussure’s colleagues after his death and based on student notes), the analysis focuses not on the use of language (called “parole,” or speech), but rather on the underlying system of language (called “langue”).
This approach examines how the elements of language relate to each other in the present, synchronically rather than diachronically. Saussure argued that linguistic signs were composed of two parts, a “signifier” (the “sound pattern” of a word, either in mental projection—as when we silently recite lines from a poem to ourselves—or in actual, physical realization as part of a speech act) and a “signified” (the concept or meaning of the word).