Modernity rests on a distinction between Us moderns and Them primitives. Them primitive might be dead and gone; they might be somewhere south of Us, in warmer, wetter climates and with darker skin. But Them is primitive, even if they are contemporaries.
The problem is, modernity spawns a continuous streams of new Us’s. Modernity is novelty, and the newer the novelty the better. Each new novelty renders the last novelty old-fashioned. Each novelty creates a new Them to contrast with Us avant-gardists, Us true moderns.
Modernity thus continuous transgresses the bounds of modernity, continuously surpasses itself. Modernity is at its essence a machine for producing the post-modern.