Definition of "rational"

The utility of valid arguments is a monument to our frailty: to the fact that we are not completely rational beings.

2001, Mark Sainsbury, chapter 1, in Logical Forms — An Introduction to Philosophical Logic, 2nd edition, Blackwell Publishing, §7, page 32

Prevention for the future is now almost universally allowed to be the only rational plea for the infliction of punishment; but this, when left to the arbitrary discretion of individuals, always has been found, and always will be found, to degenerate into the exercise of revenge for the past.

1812 The Freethinking Christians' Magazine: Volume 2 p. 21

Temperature 99.8 degrees. Pulse 104. She was quite conscious and rational at times, at others very noisy.

1867 C. Handfield Jones, Case Of Low Fever: Delirium: Incomplete Dementia. The British Medical Journal Vol. 2, No. 344, Aug. 3

The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason. The architect of modern science was himself not very modern. He was obsessed with alchemy.

2014 June 21, “Magician’s brain”, in The Economist, volume 411, number 8892

The Rationale of iudgement alſo thou shalt mke with embrodered worke of diuers colours, according to the workmanship of the Ephod of gold, hyacinth, and purple, and ſcarlet twiſe died, and twiſted ſilke.

1609, The Holie Bible, […] (Douay–Rheims Bible), Doway: Lavrence Kellam, […], Exodvs 28:15, page 234