In psychology, essentialism is used as a model for how humans understand the world. Rather than making a broader claim about how the world is, as philosophical essentialism does, psychologists instead suggest that humans sort entities into categories as if the objects had certain essential, defining properties, regardless of whether this reflects some objective reality.
Essentialism has profound implications for ethics, in that a classical essentialist believes actions can be sorted into objective right and wrong categories, since "right" and "wrong" can be defined by their essential properties. Modern essentialism takes the weaker view that individuals construct their own right and wrong and ascribe essential properties to these categories on an individual basis.
Professor Lawrence Hirschfeld gave an example demonstrating the principles of essentialism when he asked what was the essence of a tiger. He pointed out that the essential properties of a tiger cannot be defined by its number of legs or color since a tiger with a missing leg or a non-striped, albino tiger is still a tiger. These characteristics would be considered inessential, or accidental.
Essentialism contrasts with non-essentialism, the belief that an entity cannot be defined by any essential set of characteristics. Non-essentialists argue that every member of a group also has "accidental" characteristics, and, therefore, there is no such thing as an entity that has only essential properties.