Plato's idealism in psychology:

* concepts and categories - prototypes are modern version of ideal Forms

* schemas (frameworks for organizing knowledge of categories, like concepts, stereotypes and social roles) and scripts (frameworks for organizing knowledge of common actions or events, like going to restaurants or movie theaters)

* mental representations - e.g., of elephants, or Tolman's rats' cognitive maps of maze layout

* mind viewed as separate from body and brain

* intelligence and IQ tests - viewed as an attribute (often called "g" for "general intelligence"), abstracted away from actual performance of tasks and skills in real life

* personality - theories of types as in the bogus Myers Briggs MBTI yielding 16 types; or of traits like Big Five traits (“OCEAN”); more useful when you don't already know the person, otherwise real interactions give more information than abstract characterization

* abnormality as deviation from normality - so normality must be an abstraction from observed behavior

* language - Chomsky focused on abstract knowledge of rules for syntax, rather than communication via speech in actual spoken sentences

* psychological measurement theory interested in "true scores" - e.g., observed score on test or scale (e.g., of anxiety) is theorized to reflect a "true" amount of the underlying trait being measured

* statistics - focuses on the mean to represent response to an experimental treatment, even though that number may not have been obtained from any individual subject in the experimental group; as opposed to the set of actual observations whose variability is largely ignored; mean is thought to be the “real” value, standard deviation represents miscellaneous noise in data corresponding to actual observations

* generalizing from small groups to a whole population is a kind of inductive definition of an experimental treatment's effect, going from particular examples and observations to a general statement of knowledge or truth

* scientific laws in general are idealized abstract (usually mathematical) descriptions of observations

"The spirit of Plato dies hard. We have been unable to escape the philosophical tradition that what we can see and measure in the world is merely the superficial and imperfect representation of an underlying reality. Much of the fascination of statistics lies embedded in our gut feeling -- and never trust a gut feeling -- that abstract measures summarizing large tables of data must express something more real and fundamental than the data themselves." - Stephen Jay Gould (1996), The Mismeasure of Man, 2nd ed.