Rational - rationale

It is easy to confuse the spelling of the adjective rational with the spelling of the noun rationale. Don't do it!

• The basic meaning of the adjective rational, pronounced with the stress on the first syllable 'RASH-'n-'l' (IPA: /ˈræʃ ən əl/), is 'to do with [the mental power of] reason', 'to do with logical thought'. So a person can be rational, by using considered qualities of thought in decisions. (Human beings are rational creatures, and it was traditionally held, with very little basis, that men are more rational beings than women.) A decision or any other thought process may be described as rational when it is based on logical thought, or carefully considered balances of ideas.
• The noun rationale, pronounced with the stress on the last syllable 'rash-'en'AHL', /ræʃ ən ˈɑːl/ (but see the note below), means 'the reasoned explanation behind [an idea or argument, etc]', or 'the fundamental reason [for doing or thinking something]'.

Note: Until the second half of the twentieth century, the final '-e-' of rationale was sounded, 'rash-on-ALE-y'. IPA: //