Phrenology's fundamental assumptions remained constant throughout the history of the movement. They were succinctly stated by George Combe as consisting of the folowing three "fundamental principles': (1) That the brain is the organ of the mind:;; (2) That the brain is the aggregate of several parts, each subserving a distinct mental faculty; (3) That the size of the cerebral organ is, ceteris paribus, an index of power or energy of function.
Pares autem vetere proverbio, cum paribus facillime congregantur.
We may assume the superiority ceteris paribus [all things being equal] of the demonstration which derives from fewer postulates or hypotheses in short from fewer premisses; for... given that all these are equally well known, where they are fewer knowledge will be more speedily acquired, and that is a desideratum . The argument implied in our contention that demonstration from fewer assumptions is superior may be set out in universal form...