It’s common for words that share an origin to be similar in spelling. ‘Rational’ and ‘rationale’, for instance, both draw upon the idea of being reasonable or logical, with the only thing separating them on the page being that final ‘e’ (they’re also pronounced slightly differently).
Yet these words are importantly distinct, so you won’t want to confuse them in your written work. Today, we explain why a ‘rationale’ should always be ‘rational’, not the other way round!
Rational (Reasonable or Logical)
‘Rational’ is an adjective meaning ‘reasonable’ or ‘capable of exercising reason’. We therefore use it to describe something that is in accordance with or possesses reason:
As a rational person, I try to consider every possibility before reaching a conclusion.
Given the traffic in town, walking was the rational option.
I don’t think we’re going anywhere fast here… [Photo: A Verdade/wikimedia]The opposite of ‘rational’ is ‘irrational’, meaning ‘illogical’ or ‘lacking reason’. ‘Rational’ can also be made into the adverb by adding ‘-ly’ (e.g. ‘He acted rationally’).
In mathematics, you may also hear the term ‘rational numbers’. This describes numbers that can be written as a fraction or ratio, including all positive and negative integers.
Rationale (A Reason for Action)
A ‘rationale’ is a reason or argument for acting in a particular way. We might therefore say that:
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My rationale for walking is that the traffic in town makes driving too slow.
It’s either walk or go full Michael Douglas at this point…
In academic writing, you may be asked to provide a ‘research rationale’. This is simply a justification of your reasons for conducting a study and why the research is important.
Rational or Rationale?
It goes without saying that a good ‘rationale’ is supposed to be ‘rational’, since you can’t justify an action (or your research) using illogical or inconsistent arguments!
Nevertheless, ‘rational’ is an adjective and ‘rationale’ is a noun, so they’re not interchangeable and you should take care to use them correctly in your work. Remember:
Rational (adjective) = Reasonable
Rationale (noun) = A reason for action