There is no straight-forward answer to this question. Judgements of irrationality are a constant feature of our social practices but we might mean different things when we call someone irrational. Irrationality is a moving target.
It escapes clarification because it is used to express disapproval towards behaviour that is sanctioned,where the reasons why it is sanctioned change according to the aspects of human agency that are found to be problematic in a given context.
Here are some examples:
People who deny climate change may be called irrational because they have beliefs that are badly supported by evidence and conflict with our best scientific theories.
People who go and live together or get married soon after they meet may be called irrational because they make an important decision based on emotional responses that are unlikely to be a reliable guide to their future happiness.
People who sincerely report to care about, and campaign for, water conservation but take long showers may be called irrational because they appear hypocritical and their behaviour lacks consistency.
Is there anything in common among these everyday manifestations of irrationality? Is it always bad to be irrational? What does the acknowledgement of irrationality mean for human agency?
I have been interested in irrationality for a long time,and in my forthcoming book I address philosophical issues surrounding the concept, with an eye to the latest findings in the empirical sciences of the mind.
We all recognise ourselves as irrational agents at least some of the time, and we certainly spot irrationality in our fellow human agents. This strongly suggests that irrational behaviour is not the exception, an unexpected deviation from the norm that needs to be explained away, but a core feature of our behaviour. It is important to acknowledge how pervasive irrationality is, as strategies can be developed to reduce the potentially negative effects of irrationality on the acquisition of knowledge, on the pursuit of our cherished goals and on well being more generally.
Lisa Bortolotti is Professor of Philosophy at the University of Birmingham. She runs a blog called Imperfect Cognitions where different aspects of human irrationality are discussed by philosophers, psychologists and psychiatrists.
Her new book, Irrationality, is part of the Key Concepts series and published in October 2014.