Principles of Sociology : Vol. I–IV.

In 'The Principles of Sociology' Spencer rejected the sociology of Auguste Comte's positivism and made some valuable contributions to early sociology, attempting to reformulate social science in terms of evolutionary biology. A 'social organism' evolved from the simpler state to the more complex according to the universal law of evolution. Spencer's theories of laissez-faire, survival-of-the-fittest and minimal human interference in the processes of natural law had an enduring influence on thinkers and politicians such as Friedrich Hayek, Milton Friedman and Margaret Thatcher.