  A new approach to the understanding of sociological collective behaviour,
based on the framework of critical phenomena in physics, is presented. The
first step consists of constructing a simple mean-behaviour model and applying
it to a strike process in a plant. The model comprises only a limited number of
parameters characteristic of the plant considered and of the society. A
dissatisfaction function is introduced with a basic principle stating that the
stable state of the plant is a state, which minimizes this function. It is
found that the plant can be in one of two phases: the "collective phase" and
the "individual phase". These two phases are separated by a critical point, in
the neighbourhood of which the system is very sensitive to small changes in the
parameters. The collective phase includes a region of parameters for which the
system has two possible states: a "work state" and a "strike state". The actual
state of the system depends on the parameters and on the "history of the
system". The irreversibility of the transition between these two states
indicates the existence of metastable states. For these particular states, the
effect of small groups of workers or of a small perturbation in the system
results in drastic changes in the state of the plant. Other non-trivial
implications of the model, as well as possible extensions and refinements of
the approach, are discussed.
