 Mill (1843) refined the Humean Regularity Theory of causation. An effect usually occurs only due to several instantiated factors, that is, instantiated event types. He distinguishes between positive and negative factors. Let \(C_1,\) \(C_2,\) …, \(C_n\) be a set of positive factors and \(\overline{D}_1,\) \(\overline{D}_2,\) …, \(\overline{D}_m\) a set of negative factors which are together sufficient for an effect \(E\). Mill says that the totality of present positive and absent negative factors sufficient for an effect to occur is the cause of this effect. In symbols, the totality of the token events \(c_1,\) \(c_2,\) …, \(c_n\) and the absence of any token events of the types \(D_1,\) \(D_2,\) …, \(D_m\) is a cause of an occurring event \(e\) iff \(C_1,\) \(C_2,\) …, \(C_n,\) \(\overline{D}_1,\) \(\overline{D}_2,\) …, \(\overline{D}_m\) is sufficient for \(E\).