Psychological Essentialism
Psychological essentialism is the belief that a category has an immutable underlying essence which causes its observable features and licenses inference about features you have not observed. Knowing a thing is a tiger is what lets you assume things about it that nobody told you, and what makes you treat those things as fixed. Applied to objects it is often useful. Applied to people it is a fixed mindset about persons, and that is where it does its damage. The literature is genuine; the secondary account this page draws on reports it with no citations at all, which is why the page is marked mixed.
What it is
The working scheme has four criteria for an essentialist belief. Causal mechanisms, where the essence produces the surface features. Innate potential, where the essence is there from the start. Immutability, where it does not change. And inductive potential, where knowing the category tells you things you have not observed.
Alongside those sit six features of essentialist thinking: discreteness, biological basis, immutability, informativeness, consistency and inherence.
The six-feature scheme is Nick Haslam's, and the source this page draws on never names him in its prose. Haslam and Levy's 2006 paper appears in that chapter's bibliography and is never brought into the argument. Susan Gelman, Douglas Medin and Myron Rothbart, who built the developmental and social-cognitive foundations the chapter stands on, are absent from prose and bibliography alike. The identification of Haslam is this publication's, not the book's. A reader of that chapter is handed a six-part taxonomy with nobody attached to it.