ra ‧ tion ‧ al ‧ is ‧ m AC /ˈræʃ ə nəlɪz ə m/ BrE AmE noun [uncountable]
[ Word Family: noun : ↑ rationality ≠ ↑ irrationality , ↑ rationale , ↑ rationalism , ↑ rationalist , ↑ rationalization ; adjective : ↑ rational ≠ ↑ irrational , ↑ rationalist ; verb : ↑ rationalize ; adverb : ↑ rationally ≠ ↑ irrationally ]
technical the belief that your actions should be based on scientific thinking rather than emotions or religious beliefs:
philosophers who accept scientific rationalism