Brook's Law

Brook's Law is the observation, formulated by Fred Brooks in The Mythical Man-Month (1975), that adding human resources to a late software project makes it later. The law is not a psychological claim about programmer morale or a managerial claim about coordination overhead. It is a systems theorem about information topology: the time required to integrate new members into a project is a function of the number of communication channels that must be established, and the number of channels grows quadratically with team size.

Brooks distinguished two types of work in software: partitionable tasks (which can be divided among workers) and sequential tasks (which cannot). Adding people speeds up partitionable work but slows sequential work, because the new workers must be educated in the project's state before they can contribute. When a project is late, its remaining work is typically sequential — the easy partitions have already been exploited. Adding people therefore increases the sequential load (training) without increasing partitionable capacity.

The deeper systems insight is that Brook's Law applies beyond software. Any project whose coordination structure is a dense network rather than a modular hierarchy will exhibit the same nonlinearity: more participants produce more coordination overhead than productive capacity. The law is a special case of the broader principle that scaling a system requires restructuring its communication topology, not merely adding nodes to an existing graph.