You mention the term post - structuralism [as opposed to "postmodernism"?].
I wouldn't say both terms are in opposition to one another, even though poststructuralists like Derrida never identified themselves with the postmodern movement. I think the term poststructuralism is more appropriate because structuralism, contrary to modernism, encompasses the entire occidental philosophical history, as argued by Derrida in Structure, Sign and Play.
It would be easy enough to show that the concept of structure and even the word "structure" itself are as old as the episteme -that is to say, as old as western science and western philosophy-and that their roots thrust deep into the soil of ordinary language, into whose deepest recesses the episteme plunges to gather them together once more, making them part of itself in a metaphorical displacement. Nevertheless, up until the event which I wish to mark out and define, structure-or rather the structurality of structure-although it has always been involved, has always been neutralized or reduced, and this by a process of giving it a center or referring it to a point of presence, a fixed origin. The function of this center was not only to orient, balance, and organize the structure-one cannot in fact conceive of an unorganized structure-but above all to make sure that the organizing principle of the structure would limit what we might call the freeplay of the structure. No doubt that by orienting and organizing the coherence of the system, the center of a structure permits the freeplay of its elements inside the total form. And even today the notion of a structure lacking any center represents the unthinkable itself.
I think poststructuralism has a broader scope than only linguistics. Numerical cognition, for instance, is a perfect example of a highly centered structure.
In regard to post - structuralism , it could be said that post - structuralist thinkers go one step farther than structuralists. Post - structuralists do indeed establish binary oppostions, but they then attempt to "transcend" these oppositions by "subverting" them. Many post-structuralist thinkers are French: Derrida; Lacan; Foucault: and Kristeva come to my mind.
That's it. Poststructuralism is the first philosophy being conscious (I guess in the English sense ) of the omnipresence of structures in all humam episteme or cognition without a deeper urge to denounce this and replacing it by another structure, like almost all previous philosophical events.