Full Idea
Karl Popper vehemently rejected the essentialism which underpins Plato and Aristotle, taking it to be a major obstacle to political, moral and scientific progress.
Gist of Idea
Popper felt that ancient essentialism was a bar to progress
Source
report of Karl Popper (Open Society and Its Enemies:Hegel and Marx [1945]) by Thomas Mautner - Penguin Dictionary of Philosophy p.179
Book Reference
Mautner,Thomas: 'Dictionary of Philosophy' [Penguin 1997], p.179
A Reaction
This makes Popper sound like an existentialist, which seems unlikely. Modern essentialism would say the opposite about science - that hunting for external imposed laws is a red herring, and we should try to understand essences.
Related Ideas
Idea 12176 Science does not aim at ultimate explanations [Popper]
Idea 12179 Essentialist views of science prevent further questions from being raised [Popper]