Certain
Certain adjective - Not capable of being challenged or proved wrong.
Usage example: up to this point there's been no certain evidence that a crime has been committed
Speculative is an antonym for certain.
Speculative
Speculative adjective - Existing only as an assumption or speculation.
Certain is an antonym for speculative.
Both words in one sentence
- Back in the 80s a magazine made a speculative guess on what certain then-current stars would be like in the future.
Source: Funny Aneurysm Moment / Music - In Speculative Fiction, as in Real Life, technology is designed with certain unquestioned assumptions: The user has the normal number of appendages, is within a certain generous range of sizes, can withstand so many G's of acceleration.
Source: Operator Incompatibility -
In certain works, especially kids shows or more whimsical Speculative Fiction the City of Adventure, the place where our heroes live has a name that fits the premise, feel or ethos of the show.
Source: Premiseville
Cite this Source
Speculative and Certain. (2016). Retrieved 2026, July 21, from https://thesaurus.plus/related/certain/speculative
Certain & Speculative. N.p., 2016. Web. 21 Jul. 2026. <https://thesaurus.plus/related/certain/speculative>.
Speculative or Certain. 2016. Accessed July 21, 2026. https://thesaurus.plus/related/certain/speculative.
Google Ngram Viewer shows how "certain" and "speculative" have occurred on timeline