illogical

Etymology

It is formed from English il- + logical,^{[2][3][4][5][6]} the prefix being the form that in-, "not", takes before l.^[7][5] Its base comes from logic, which goes back through Old French logique and Latin logica to Ancient Greek λογική (logikḗ, “the reasoning art”), from λόγος (lógos, “reason, word”).^[7]

Earliest recorded meaning

Not logical; contrary to logic, or ignorant of sound reasoning: 1588, in Abraham Fraunce's Lawiers Logike.^[2] Merriam-Webster's Unabridged also gives 1588,^[4] Etymonline the 1580s^[7] and Dictionary.com 1580–90.^[5]

Semantic evolution

The word has kept its meaning, applied both to persons and to reasoning.^[2][4] Johnson (1755) gave the two uses separately: "ignorant or negligent of the rules of reasoning", quoting Walton on a dissenter who argued with Sanderson, and "contrary to the rules of reason".^[6] The adverb illogically is recorded from the mid-17th century and the noun illogicality from the mid-19th.^[3]

Timeline

• 1588 – not logical; of a person, reasoning unsoundly.^[2][4]
• mid 17th century – the adverb illogically.^[3]
• mid 19th century – the noun illogicality.^[3]

Meanings

Adjective

1. Contrary to or lacking logic; senseless or unreasonable: It seemed illogical to repaint the fence before the storm.^[8][4][2]
2. Of a person or argument, reasoning unsoundly or disregarding the principles of logic.^[4][8][6]

Word family

• illogicality
• illogically
• illogicalness

Related words

• logic
• logical
• logos

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
4. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ a b c Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
6. ^ a b c Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
7. ^ a b c Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
8. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins