Phrenology's practical uses split sharply between reform and prejudice, sometimes within the same movement. Franz Joseph Gall himself argued that criminal behavior reflected an overdeveloped faculty rather than moral wickedness, a view Edinburgh phrenologist George Combe carried further into a genuine prison and education reform movement, arguing offenders should be assessed and rehabilitated according to their phrenological profile rather than simply punished. At the same time, from the early nineteenth century onward, phrenology was widely used to construct and justify racial and gender hierarchies, with practitioners measuring skulls from different populations and ranking them by criteria that reproduced their own prejudices; this racialized use of skull science persisted, in various forms, into other pseudoscientific craniometry.
As a scientific claim, phrenology never survived controlled comparison. No study has found that skull shape reliably predicts the underlying brain's structure closely enough to support reading it from outside, and no blinded comparison of phrenological readings against subjects' actual behavior has found phrenologists performing above chance. Its scientific credibility collapsed through the later nineteenth century, accelerated by real advances in neurology, including Paul Broca's 1861 identification of a brain region tied to speech production, which showed that functional localization in the brain was real and demonstrable through careful clinical study rather than skull measurement. Phrenology is universally treated as pseudoscience today, but its central intuition, that different brain regions handle different functions, survived it entirely, discovered again by a method Gall and Spurzheim never used.