For almost all graphs H, almost all H-free graphs have a linear homogeneous set Ross Kang, CWI There have been various structural attacks upon a conjecture of Erdos and Hajnal from extremal graph theory. This notorious open problem is concerned with understanding how the exclusion from G a fixed graph H as an induced subgraph affects the maximum size of a homogenous set (a clique or stable set) in G. I will focus on recent asymptotic, probabilistic formulations of the conjecture, proved using Szemerédi regularity, one of which is joint work with Colin McDiarmid, Bruce Reed and Alex Scott.