/ ˌræʃəˈnɑːl; NAmE -ˈnæl/ noun
rationale (behind / for / of sth) ( formal ) the principles or reasons which explain a particular decision, course of action, belief, etc.
SYN reason :
What is the rationale behind these new exams?
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WORD ORIGIN
mid 17th cent.: modern Latin , neuter (used as a noun) of Latin rationalis endowed with reason, from ratio(n-) reckoning, reason, from rat- reckoned, from the verb reri .