The aim of this paper is to examine the notion of social mechanisms by comparison with the notions of evolutionary and physical mechanisms. It is argued that social mechanisms are based on trends, and not lawlike regularities, so that social mechanisms are different from mechanisms in the natural sciences. Taking as an example of social causation the abolition of the slave trade, this paper argues that social mechanisms should be incorporated in Weber's wider notion of adequate causation in order to achieve their explanatory purpose.