A powerful argument for anti—reductionism turns on the premise that the biological, behavioral, and social sciences are, in the way that they explain their characteristic subject matters, in some sense autonomous from physics. The argument is formulated and strengthened in this paper, and then undermined by showing that a reductionist account of explanation is not only consistent with, but provides a compelling account of, explanatory autonomy. Two kinds of explanatory abstraction, objective and contextual, play important roles in the story.