Cohort

A cohort is a small group that forms inside a stigmergic movement around a task or a shared expertise, works and then comes apart. How it organizes internally is entirely up to the people in it, and Marsh is deliberate about leaving that open. A cohort can be a couple of friends or a full cooperative and it will still be part of the movement, on one condition: the work it produces stays transparent and free for anyone else to use or build upon. That condition is what distinguishes a cohort from an organization. The failure mode is ownership. A group that begins to claim a job or a whole movement as its own has stopped being a node and become an obstacle, which is why nobody in a cohort is a permanent assigned member of any job. Resilience comes from duplication rather than from assignment. Several cohorts forming over the same task means the task survives any one of them failing or leaving, and street medics and translator brigades are the examples Marsh gives, groups with structures simple enough that they can be relied upon and still be replicated easily. People self-assign to where their skills are needed and move in and out according to their own availability. The result is structure without fixed hierarchy, scalable and fluid enough to reorganize mid-event. A street medic team formed before a protest can be handed kits and stations on the day, and when somebody leaves a station another steps in, with the same structure available for the next event and no permanent post attached to anyone.

A Roman cohort was a standing unit of a legion, roughly 480 men. Epidemiology and the social sciences use the word for a group sharing a defining characteristic who are followed over time, as in a birth cohort or a cohort study. Education borrowed it for a set of students moving through a programme together, and technology companies use it for users grouped by signup date. Every one of these depends on fixed membership, since the whole point of a research cohort is that the same people stay in it. Marsh's cohort inverts that. Membership is temporary by design, the group is expected to dissolve and its legitimacy rests on the openness of what it produces rather than on who belongs to it.