Lehman's laws of software evolution

In software engineering, the laws of software evolution refer to a series of laws that Lehman and Belady formulated starting in 1974 with respect to software evolution. The laws describe a balance between forces driving new developments on one hand, and forces that slow down progress on the other hand. Over the past decades the laws have been revised and extended several times.

Observing that most software is subject to change in the course of its existence, the authors set out to determine laws that these changes will typically obey, or must obey in order for the software to survive.

In his 1980 article, Lehman qualified the application of such laws by distinguishing between three categories of software:

The laws are said to apply only to the last category of systems.

All told, eight laws were formulated:

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