Kacelnik: Meanings of Rationality (preprint) Meanings of Rationality

The concept of rationality differs between psychology, philosophy, economics and biology. For psychologists and philosophers, the emphasis is on the process by which decisions are made: rational beliefs are arrived at by reasoning and contrasted with beliefs arrived at by emotion, faith, authority or arbitrary choice. Economists emphasise consistency of choice, regardless of the process and the goal. Biologists use a concept that links both previous ideas. Following Darwin's theory of natural selection, they expect animals to behave as if they had been designed to surpass the fitness of their conspecifics and use optimality to predict behaviour that might achieve this. I introduce the terms PP-rationality, E-rationality and B-rationality to refer to these three different conceptions, and explore the advantages and weaknesses of each of them. The concepts are first discussed and then illustrated with specific examples of research in bird behaviour, including New Caledonian crows' tool design, hummingbirds' preferences between flowers and starlings' choices between walking and flying. I conclude that no single definition of rationality can serve the purposes of the research community but that agreement on meanings and justifications for each stand is both necessary and possible.