This is an extensively revised article on one of the more interesting (and difficult) philosophers of the 20th century, Jacques Derrida. I won't pretend to be able to speak with any authority on his work. But here's the ten-cent perspective of at least some of it: there are no simple irreducible concepts. Every concept (every work, every perception) contains both itself and the negation of itself inherently in its presentation. For example, "what is happening right now is also not different from every other now I have ever experienced. At the same time, the present experience is an event and it is not an event because it is repeatable." Or for example, "for a decision to be just, not only must a judge follow a rule but also he or she must 're-institute' it, in a new judgment. Thus a decision aiming at justice (a free decision) is both regulated and unregulated." What's important here (to me) is that you can't separate these different aspects of the concept; they are one and the same thing.