underlying assumption

Translations
основное предположение
The underlying assumption of the study was later proven to be incorrect.
Основное предположение исследования позже оказалось неверным.
Definitions
An underlying assumption is a belief or idea that is taken for granted and serves as a foundation for reasoning, arguments, or actions, often without being explicitly stated.
Words
assumption

noun
предположение
underlying

adjective
основной