Party activists face a coordination problem: a critical mass (a barrier to coordination) must advocate a single policy alternative if the party is to succeed. The need for direction is the degree to which the merits of the alternatives respond to the underlying mood of the party. An individual’s ability to assess the mood is his sense of direction. These factors combine to form an index of both the desirability and the feasibility of leadership: we call this index Michels’ Ratio. A sovereign party conference gives way to leadership by an individual or oligarchy if and only if Michels’ Ratio is sufficiently high. Leadership enhances the clarity of intra-party communication, but weakens the response of policy choices to the party’s mood.