Teleology

You, dear reader, are a goal-directed system. Arguably, the snake plants and thermostats in my home are goal-directed systems too. On a much larger scale, the water and rock cycles that you learnt about in science classes at school might well be goal-directed systems. If these are all goal-directed systems, it is appropriate to ascribe functions to their parts. For example, the function of a thermostat’s bimetallic strip is to gauge temperature.

By describing these examples in this way, we appear to be ascribing teleological properties to such systems. The term ‘teleology’ is derived from ‘telos’, the Greek word for ‘end’ or ‘goal’. Teleology as a discipline is thus the study of ends and goals, as well as the related concepts of functions, aims, and purposes. What all these phenomena have in common is that they involve means–end relations of some sort. For instance, a goal-directed system acts in order to bring about a certain end (its goal); something with a function acts in order to contribute to the end (or goal) of a system; and something with a purpose typically acts in such a way as to achieve that purpose. It is also plausible that these teleological concepts are interrelated in various ways. For example, according to a theory explored in Section 2, the concepts of function and goal are intimately connected: something performs a function precisely when it contributes towards a goal of a system.

Teleology is not only of interest to metaphysicians, and I hope this contribution to the Elements series will encourage readers to engage with a range of theoretical themes across philosophy, science, and technology. Moreover, my aim is not only to explain teleology as a discipline, but also to provide my novel take on how teleology arises in the natural world. It is important to understand teleology because teleological concepts are employed by many explanations that are offered both in everyday contextsFootnote 1 as well as in the special sciences. Biological examples are often used in discussions of teleology, and I will often employ such examples in this Element. However, talk of functions is also common in (for instance) biochemistry, medicine, psychology, the social sciences and technology, as well as the emerging area of artificial intelligence (AI). Functional explanations are widespread in many of these areas, and many scientists regard such explanations as indispensable (Reference Nagel Nagel 1979: 276). One hallmark of many functional explanations is that they are forward-looking: they explain the presence, character, or activity of an item by reference to some possible future outcome that the item tends to bring about. A mundane example of such an explanation is that a knife is sharp because the knife’s function is to cut; but many functional explanations are more surprising than this and reflect important scientific discoveries. On the front page of the module guide for a metaphysics course on which I was once a teaching assistant, there was a picture of a donkey curling up its top lip. Amusingly, it appeared that the donkey was laughing or talking – a reference, I suspect, to David Lewis’s famous example of donkeys talking in distant possible worlds. I always thought the donkey’s pose was accidental, but later I learnt that the function of this lip movement in donkeys is to expose the vomeronasal organ, which has the further function of sensing pheromones in the air.Footnote 2 Importantly, because these functions contribute to the survival of donkeys in various respects, those functions also help to explain why these types of lip and organ are there in the first place. Thus, many philosophers of science (e.g., Reference Garson Garson 2017, Reference Garson 2019a, Reference Garson 2019b; Reference Mitchell Mitchell 1993; Reference Neander Neander 1991) have emphasized that many, or even all, biological functions have an important historical or ‘backward-looking’ explanatory role. We shall explore the details in Section 2, where we discuss the selectionist, causal role and goal-contribution conceptions of function. For current purposes, the important point is just that discoveries of various functional explanations are often startling, illuminating, and significant.

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