Fallacious
Fallacious adjective - Not using or following good reasoning.
Usage example: it's fallacious to say that something must exist because science hasn't proven its nonexistence
Logical is an antonym for fallacious.
Logical
Logical adjective - According to the rules of logic.
Usage example: the lawyer won the case with a logical argument about the motives of the suspect
Fallacious is an antonym for logical.
Both words in one sentence
- However, one must keep in mind that—depending on the surrounding circumstances—a deductively fallacious argument may still, nonetheless, be a reasonable and (inductively) logical argument that has decent prospects of being true despite the deductive logic being invalid.
Source: Logical Fallacies -
Showcased on the "Germany" episode of QI as "Godwin's Rule", giving an example of Hitler's love of animals (and disgust of fox hunting) as a fallacious reason to keep fox hunting legal, though this wiki considers that a wholly separate logical fallacy: Hitler Ate Sugar.
Source: Godwin's Law - Their method of communication is structured in such a way that any logical error is necessarily a syntactical error as well, meaning that if a group of Lambertians is told a fallacious argument, they will notice the error within a matter of minutes and then tell you what's really true.
Source: Can't Argue with Elves
Cite this Source
Logical and Fallacious. (2016). Retrieved 2026, August 13, from https://thesaurus.plus/related/fallacious/logical
Fallacious & Logical. N.p., 2016. Web. 13 Aug. 2026. <https://thesaurus.plus/related/fallacious/logical>.
Logical or Fallacious. 2016. Accessed August 13, 2026. https://thesaurus.plus/related/fallacious/logical.
Google Ngram Viewer shows how "fallacious" and "logical" have occurred on timeline