From Longman Dictionary of Contemporary Englishunderlying cause/principle/problem etcunderlying cause/principle/problem etcCAUSEthe cause, idea etc that is the most important, although it is not easily noticed the underlying causes of her depression There is an underlying assumption that younger workers are easier to train. → underlying

Examples from the Corpus

underlying assumption• Both of these expressions, however, have rather different underlying assumptions.• Neither is really aware of his underlying assumptions.• The underlying assumption appears to be one of integration.• In the classroom, cultural analysis encourages students to examine for themselves the underlying assumptions in the texts they are studying.• The underlying assumption is that gradual hormonal decline is bad because some physical functions decline at the same time.• While the criticisms vary, the underlying assumption is that overall economic growth has been speeding up.• First, its underlying assumption is that the number of entities that the world consists of is finite.