This should be called the principle of the separation of conception from execution, rather than by its more common name of the separation of mental and manual labor (even though it is similar to the latter, and in practice often identical).  This is because mental labor, labor done primarily in the brain, is also subjected to the same principle of separation of conception from execution: mental labor is first separated from manual labor and, as we shall see, is then itself subdivided rigorously according to the same rule (79).