who invented causal spaces in order to "admit structures which can be very different from a manifold". Causal spaces are defined axiomatically, by considering not only causal precedence, but also chronological precedence.

The program of causal sets is based on a theorem by David Malament, extending former results by Christopher Zeeman, and by Stephen Hawking, A. R. King and P. J. McCarthy. Malament's theorem states