rationality

Etymology

It is borrowed from Late Latin ratiōnālitās (“faculty of reasoning”), used by Tertullian in the early 3rd century and, in mathematics, for the property of a quantity of being rational in a British source of 1267,^[2] formed from Latin ratiōnālis (“of or belonging to reason, reasonable”) and -tās.^{[2][3][4][5][6]} Etymonline also names French rationalité as a source,^[3] but the OED dates the French word to the 19th century (13th century in Old French as racionalite) and compares Italian razionalità, recorded before 1406.^[2] The Latin adjective comes from ratiō (“reckoning, calculation, reason”).^[4][3] Middle English had instead racionabilite (“the faculty of reason”), from ratiōnābilitās, in the early 15th century.^[3]

Earliest recorded meaning

In mathematics, the property of a number or quantity of being rational: 1570, in H. Billingsley's translation of Euclid's Elements.^[2] Dictionary.com dates the word to 1560–70^[7] and the Shorter Oxford to the late 16th century.^[6]

Semantic evolution

The general sense, the possession of reason, followed in 1628, in T. Spencer's Art of Logick;^[2][4] Etymonline dates it to the 1620s.^[3] From 1637 the word also meant the quality of being in accordance with reason, which Etymonline dates to the 1650s;^[2][3] from 1654 it could be counted, for a reasonable view or practice; from 1660 it also named a tendency to look at everything from a purely rational point of view.^[2] A sense equal to rationale was used rarely from 1646 to 1701.^[2] Johnson (1755) gave "the power of reasoning" and "reasonableness".^[8] In economics it names the assumption that a consumer weighs all possible combinations of goods and prices.^[9] In Ayrshire Scots it was recorded in 1890 for sense or reason returning to someone.^[10]

Timeline

• 1570 – in mathematics, the property of being rational.^[2]
• 1628 – the possession of reason, the ability to reason.^[2][4]
• 1637 – the quality of being in accordance with reason.^[2]
• 1646 – a rationale (obsolete by 1701).^[2]
• 1654 – a rational view or practice, often in the plural.^[2]
• 1660 – the tendency to regard everything from a purely rational point of view.^[2]

Meanings

Noun

1. The quality or state of being rational, logical or reasonable: She questioned the rationality of the new rules.^[9][4][2]
2. The possession or use of reason; the ability to reason.^[9][2][8]
3. A rational or reasonable opinion, view or practice; often in the plural.^[9][2]
4. (mathematics) The property of a number or quantity of being rational.^[2][6]
5. (economics) The assumption that a person compares all possible combinations of goods and their prices when buying.^[9]

Word family

• antirationality
• irrationality
• nonrationality

Related words

• rational
• ratio
• reason
• rationale

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
6. ^ a b c Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
7. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
8. ^ a b Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
9. ^ a b c d e Collins English Dictionary (2023), Glasgow: HarperCollins
10. ^ Wright, Joseph, ed. (1898–1905), The English Dialect Dictionary, 6 vols., Oxford: Henry Frowde; via EDD Online 4.0, University of Innsbruck (CC BY 4.0)