The best course would seem to be to deal directly with the questions raised in the Introduction. But to deal with them in a fruitful way requires some background. To explain patterns of justice, I shall use a form of explanation that refers to a basic level of social structure plausibly called material. So much, though, has gone under the name of materialistic explanation that the key concepts have long since lost any firm meaning. To move ahead requires that the concepts be redeemed. Only in Part Two will I return to questions about justice.

The view of explanation put forward in Part One posits two tiers. Historical narrative, replete with agents and their effects, belongs to one of the tiers. The other tier is less often appealed to, but it is perfectly obvious from a consideration of the natural sciences. It is the tier of structures lying behind sequences of agents and effects. It is inappropriate to speak of these structures as themselves agents, and it is important to distinguish the way structures determine things from the way agents do.

To call a form of explanation materialist will be taken here to be a claim about structure rather than agency. It is a kind of explanation that uses a material structure for its second tier, whatever the agencies might be.