Leo van Lier (2004). «Relations». e-Study Guide for: Handbook of Psychology, Volume 6: Developmental Psychology: Psychology, Human development. Springer. p. 4. ISBN978-1402079047. «a relationship between an organism and the environment that signals an opportunity for or inhibition of action».
Don Norman (2013). The Design of Everyday Things (Revised and expanded edición). Basic Books. p. 11. ISBN978-0465050659. «An affordance is a relationship between the properties of an object and the capabilities of the agent that determine just how the object could possibly be used.»