All 5 Uses

rational
in
Delirium, by Lauren Oliver
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Of course that's one of the reasons it's so dangerous: It affects your mind so that you cannot think clearly, or make rational decisions about your own well-being.†
p. 3.1

rational = reasonable
Part of my brain—the rational, educated part, the logical me part—screams, Blue!†
p. 35.1
Everything rational, right, and good is screaming for me to turn around and go upstairs, but some stubborn inner center keeps me moving forward.†
p. 118.9
PHASE THREE (CRITICAL)
difficulty breathing
pain in the chest, throat, or stomach
difficulty swallowing; refusal to eat
complete breakdown of rational faculties; erratic behavior; violent
thoughts and fantasies; hallucinations and delusions†
p. 147.8
That is the single idea in my mind, the one that has supplanted the possibility of all other rational thought.†
p. 341.8 *

Definitions:

(1) (rational as in: rational behavior)
reasonable, able to think clearly, or based on logic rather than emotion
(2) (meaning too rare to warrant focus)
More rarely, rational numbers in mathematics are numbers that can be expressed as a fraction consisting of only an integer in the numerator and denominator. For example, 1/3 is a rational number while pi is an irrational number.