Synthese (2011) 183:409–427 DOI 10.1007/s11229-011-9870-3 Mechanisms revisited James Woodward Received: 7 October 2010 / Accepted: 3 January 2011 / Published online: 12 January 2011 © Springer Science+Business Media B.V. 2011 Abstract This paper defends an interventionist treatment of mechanisms and contrasts this with Waskan (forthcoming). Interventionism embodies a difference- making conception of causation. I contrast such conceptions with geometrical/ mechanical or “actualist” conceptions, associating Waskan’s proposals with the latter. It is argued that geometrical/mechanical conceptions of causation cannot re- place difference-making conceptions in characterizing the behavior of mechanisms, but that some of the intuitions behind the geometrical/mechanical approach can be captured by thinking in terms of spatio-temporally organized difference-making in- formation. Keywords Mechanism · Interventionist theory of causation · Difference-making · Perception of causation 1 Introduction I’m pleased to have this opportunity to discuss Jonathan Waskan’s “Mechanistic Expla- nation at the Limit”. In what follows I explore some issues dividing the interventionist treatment of mechanisms in Woodward, 2004 from the alternative suggestions in Was- kan’s essay. Sections 1–4 lay out the basic ideas of the interventionist framework and the contrast between two different conceptions of causation, which I call difference- making and geometrical/mechanical. Sections 5–8 then comment on Waskan’s ideas. It is widely agreed that in many areas of science information about “mechanisms” plays a central role: the identification of mechanisms is a major goal of theory con- struction, information about mechanisms is important in causal explanation and so J. Woodward (B ) University of Pittsburgh, Pittsburgh, PA, USA e-mail: jfw@pitt.edu 123