Deconstruction assumptions

In deconstruction the basic structuralist principle of difference is located ontologically as well as semiotically: at the very point of beingness of every thing there is difference -- or différance -- because only through différance is one thing not another thing instead. Différance comes before being; similarly, a trace comes before the presence of a thing (as anything which is is itself by virtue of not being something else, by differing, and that which it differs from remains as a trace, that whose absence is necessary for it to be); so too writing precedes speech -- a system of differences precedes any location of meaning in articulation. See my summary of Derrida, Différance.
Deconstruction, as do other poststructural theories, declines the structuralist assumption that structural principles are essences -- that there are universal structural principles of language which exist 'before' the incidence of language. (The emphasis on the concrete, historical and contingent in opposition to the eternalities of essence reveals one of deconstruction's filiations with existentialism.) All 'principles' of existence (i.e., of experience) are historically situated and are structured by the interplay of individual experience and institutional force, through the language, symbols, environment, exclusions and oppositions of the moment (and of the previous moments through which this one is constructed). Structures are historical, temporary, contingent, operating through differentiation and displacement.