Yves Charles Zarka seeks to show that Hobbes conceives of causes as events and that the progressive constitution of his theory of causality, from the Short Tract up to De corpore, introduces all elements required of a theory of event. Such a theory raises special problems as to the nature of rationality, theological foundations of a system of events and the status of politics in a physical universe governed by necessity. Some of those special problems include the well-known objections raised by Cudworth, Bramhall and Leibniz. Zarka stresses in particular the importance of the debate between Hobbes and Bramhall on liberty, necessity and chance in the formulation of those problems. One thesis of this paper is that such a theory of event can explain why Hobbes’s materialism can be changed, in his political thought, into its opposite.