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
Invalid is a synonym for fallacious in false topic. In some cases you can use "Invalid" instead an adjective "Fallacious", when it comes to topics like correct, illogical, null and void. popular alternative
Invalid
Invalid adjective - Not being in agreement with what is true.
Usage example: that's an invalid assumption on your part
Fallacious is a synonym for invalid in false topic. You can use "Fallacious" instead an adjective "Invalid", if it concerns topics such as correct, worthless, illogical, null and void. popular alternative
Mutual synonyms
Both words in one sentence
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Instead of meaningless numerical symbols, it's an invalid proof that involves dividing by zero, perhaps to complement the scientist's fallacious reasoning.
Source: E = MC Hammer - 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
Cite this Source
Invalid and Fallacious. (2016). Retrieved 2026, August 14, from https://thesaurus.plus/related/fallacious/invalid
Fallacious & Invalid. N.p., 2016. Web. 14 Aug. 2026. <https://thesaurus.plus/related/fallacious/invalid>.
Invalid or Fallacious. 2016. Accessed August 14, 2026. https://thesaurus.plus/related/fallacious/invalid.
Google Ngram Viewer shows how "fallacious" and "invalid" have occurred on timeline