Please forgive the length of this Response. Much like Derrida, I had a hard time finding a stopping point.

I am sympathetic to people who have no patience for Derrida's style, but I do think there is much valuable substance there. He was in the position of trying to make conclusive statements about the intellectual projects of modernity while denying the legitimacy of 'definitive' (discursive-stopping) statements about anything.

He definitely contributed the development of the Postmodern perspective, which has resulted in several insights that (understanding how little it is worth) I accept as confirmed. (For better or worse, like most postmodernists have, I have fallen in love with single quote marks.)

(1) There can be no 'objectivity', in the sense of a state of mind in any person in which no extraneous (to the topic at hand) subjective influences are operative.

(2) Once words are written their author has no more authority re. their significance ('what they signify') than anyone else.

(3) 'Deconstruction': the process of uncovering unstated assumptions, suppositions, etc. (which has gone on before, as critical thinking, but 'deconstruction' is particularly focused on uncovering arbitrary, illegitimate devaluations of the 'other' that lie in the depths of people's output).

(4) Human relations have always been rife with relations of power, to include the power of deciding what is truth and what must be accepted as knowledge. (more Foucault than Derrida, but him, too)

(5) (Therefore) the ultimate 'emancipation' is the recognition that every human being is one's own judge of what is true and what is to be accepted as knowledge.

(6) So we can forget about the existence of universals, and especially the use of them to legitimate structures of power, to include political and economic systems. (As individuals, most postmodernists have favored political democracy and tended to favor socialism and even Marxism for the sake of a recognition of equality. as a governing value, even though they cannot claim it as a universal value that must be accepted by all.)

Personally, I disagree with postmodernists' claim that science per se counts as a 'structure of power' because as a process it seeks to avoid arbitrariness in outcomes (though among the human beings who comprise the scientific community that ideal of non-arbitrariness can be compromised). The same can be said of 'the rational' more generally.

To my mind, postmodernists have joined with modernists in mistakenly identifying 'reason' with 'the rational'. They are not the same thing. To be strictly rational, reasoning must be restricted to matters of material existence, as in science--though even there, due to (1), above, the shorter the chain of reasoning, the better. 'Reason' (chains of logically coherent statements related to a particular topic of discussion) can be employed in reference to beliefs (either sacral/theological or secular/ideological), which can only be extra-rational. Reasoning related to 'the extra-rational' cannot be strictly rational.