Association: one term, five concepts

'Association' is certainly one of the most prevalent terms in the study of mind, brain and behavior. It applies to actions, stimuli, neurons, brain areas, ideas, words, etc. However, we argue that this term carries qualitatively different meanings, a largely underappreciated fact. Based on a review traversing neuroscience, psychology, computer science and linguistics, we delineate and characterize five categories of usage, expressing five distinct notions of associative link which ought to be distinguished. We show how these concepts improve polysemy and synonymy issues, and together constitute a useful set of descriptive tools for the associationist framework. As they allow more transparent articulation of results and theories concerned with associations in both biological and artificial systems, they facilitate comparison of findings from different fields. The proposed terminology aims at promoting dialogue and interdisciplinary collaboration.