What does Derrida’s différance actually claim about meaning?
I teach the terminale philosophy class in a Dakar lycée. Every year one or two bright students discover Derrida online and come to class announcing that “there is nothing outside the text”, which they take to mean that nothing is real except words. The others are either impressed or furious.
I'd like to explain it properly, and I'll admit my own training was more Descartes and Senghor than Derrida. I know that Saussure argued that a sign is arbitrary and that meaning comes from differences within the system of signs. I know Derrida coined différance, with an “a”, from that background.
Can someone explain clearly: what is différance, what does the famous line about the text actually say, and is it a claim about language only, or about reality as well?