Which term refers to something that combines both an idea and its contrasting idea?

The term that best refers to something that combines both an idea and its contrasting idea is antithesis. Antithesis specifically highlights the juxtaposition of contrasting ideas within a single statement or passage, effectively emphasizing the opposition between those ideas. By presenting both perspectives, it enriches the meaning and depth of the text.

A balanced sentence can involve a parallel structure, but it doesn't necessarily imply the direct contrast of ideas as effectively as antithesis does. An oxymoron is a figure of speech that combines contradictory terms, but it typically does so within a singular phrase rather than conveying a full contrasting idea in a broader context. An allusion refers to an indirect reference to a person, event, or literary work, which does not pertain to the combination of contrasting ideas.

Therefore, antithesis is the term most aligned with the concept of blending an idea with its opposing idea, allowing for a nuanced exploration of themes and arguments.