The late, interesting-if-not-great Palestinian-Jewish-British socialist Tony Cliff said that the essential contradiction of Marxism lies between "the emancipation of the working class is the act of the working class" and "the ideas of the ruling class are the ideas of society". Can I add another very vital contradiction, for those of us who understand Foucault, Lacan, Crowley and Robert Anton Wilson on the link between language, reality and power:
Thesis: "Every identity within capitalism is constructed by capitalism, and there is no outside to capitalism."
Antithesis: "Capitalism is an internally contradictory unity prone to ever-worsening crises which can only be delayed, not avoided."
If only the first were true, there is no point to anything and we might as well have a good time until the oceans rise. If the second is true, there is no need to do anything and we only need to wait until the thing falls over. But since BOTH are true, we need to find a way to operate IN capitalism while realising that the identities it gives us are social relations and are NOT REAL, and finding ways to sharpen the contradictions in such a way that the next world-system is socialism rather than barbarism. Actually, that might be another contradiction:
Thesis: "Capitalism alienates human labour and requires us to play identity-games of oppression, exploitation and psychic injury."
Antithesis: "There is no outside to capitalism except death and insanity."