The 4th Way cosmology sees all processes as divided in seven stages, often denoted by the notes from do to si (ascending) or do to re (descending)
For example, the metabolism of man is described as as three food octaves, corresponding to how 1. physical food is transformed by the organism, 2. how air is transformed by the organism and lastly 3. how impressions are transformed by the organism.
An octave has two special intervals called shocks. These are the ones between mi and fa and si and the do of the next octave. These correspond to the absence of the black key on the piano keyboard. A process proceeds through the stages denoted by the notes if it has enough initial impetus. However, the process does not keep its original direction if left to itself. Usually, the process also needs an extra impulse from outside to proceed past the shock between mi-fa or si-do. Lack of understanding of the Law of Seven is, according to the 4th Way, the principal reason why human plans almost never reach their goal and why activities usually turn into their antithesis. One example is revolution against tyranny automatically turning into more tyranny.
According to Gurdjieff, there exists an objective way of dividing all processes, from cosmic to social to mental to biological into octaves. This division is according to Gurdjieff, the only objective basis for the notion of time. A few examples of this division are provided in literature but generally man has no capacity or insight for seeing this division in nature and practical application of this law is elusive.
Ouspensky's In Search of the Miraculous contains the best structured presentation of octaves and the Law of Seven. Mouravieff also comments on octaves and how they relate to time and the progress of entropy, a sort of winding down of the universe.
See Law of Three.