Abstract
Are the relations between the property of a thing and its related disposition to react in certain ways, and between the triggering of that disposition and the consequent effect, necessary? Harré and Madden, in their analysis of causal powers, said they are, but their arguments are not persuasive. Humeans like Simon Blackburn deny it. I criticize the Humean position, and argue afresh for their necessity. I note that David Lewis' analysis of causation requires their necessity, though as a confessed Humean he has not admitted this.