Assumption
Assumption noun - Something taken as being true or factual and used as a starting point for a course of action or reasoning.
Usage example: your argument is faulty because it's based on erroneous assumptions
Theory is a synonym for assumption in opinion topic. In some cases you can use "Theory" instead a noun "Assumption", when it comes to topics like conjecture, supposition, reason, presumption. popular alternative
Theory
Theory noun - An idea that is the starting point for making a case or conducting an investigation.
Usage example: set out to prove her theory that people can't really taste any difference between colas, so they buy according to the product's image
Assumption is a synonym for theory in hypothesis topic. You can use "Assumption" instead a noun "Theory", if it concerns topics such as opinion, conjecture, reason. popular alternative
Mutual synonyms
How words are described
Both words in one sentence
- There's the assumption and theory by some fan authors that the Warden or Mistress (or both) may secretly have feelings for the other.
Source: Fanon / Western Animation - The plan makes the false assumption that modern humans are genetically identical to their stone-age ancestors, ignoring modern evolutionary theory.
- Subverted on The Big Bang Theory when the girls take Sheldon out ballroom dancing, under the assumption that he'll be an awkward mess.
Source: Sucks At Dancing
Cite this Source
Theory and Assumption. (2016). Retrieved 2026, July 20, from https://thesaurus.plus/related/assumption/theory
Assumption & Theory. N.p., 2016. Web. 20 Jul. 2026. <https://thesaurus.plus/related/assumption/theory>.
Theory or Assumption. 2016. Accessed July 20, 2026. https://thesaurus.plus/related/assumption/theory.
Google Ngram Viewer shows how "assumption" and "theory" have occurred on timeline