There are hundreds of things we do – repeatedly, routinely – every day. We wake up, check our phones, eat our meals, brush our teeth, do our jobs, satisfy our addictions. In recent years, such habitual actions have become an arena for self-improvement: bookshelves are saturated with bestsellers about ‘life hacks’, ‘life design’ and how to ‘gamify’ our long-term projects, promising everything from enhanced productivity to a healthier diet and huge fortunes. These guides vary in scientific accuracy, but they tend to depict habits as routines that follow a repeated sequence of behaviours, into which we can intervene to set ourselves on a more desirable track.

The problem is that this account has been bleached of much of its historical richness. Today’s self-help books have in fact inherited a highly contingent version of habit – specifically, one that arises in the work of early 20th-century psychologists such as B F Skinner, Clark Hull, John B Watson and Ivan Pavlov. These thinkers are associated with behaviourism, an approach to psychology that prioritises observable, stimulus-response reactions over the role of inner feelings or thoughts. The behaviourists defined habits in a narrow, individualistic sense; they believed that people were conditioned to respond automatically to certain cues, which produced repeated cycles of action and reward.

The behaviourist image of habit has since been updated in light of contemporary neuroscience. For example, the fact that the brain is plastic and changeable allows habits to inscribe themselves in our neural wiring over time by forming privileged connections between brain regions. The influence of behaviourism has enabled researchers to study habits quantitatively and rigorously. But it has also bequeathed a flattened notion of habit that overlooks the concept’s wider philosophical implications.

Philosophers used to look at habits as ways of contemplating who we are, what it means to have faith, and why our daily routines reveal something about the world at large. In his Nicomachean Ethics, Aristotle uses the terms hexis and ethos – both translated today as ‘habit’ – to study stable qualities in people and things, especially regarding their morals and intellect. Hexis denotes the lasting characteristics of a person or thing, like the smoothness of a table or the kindness of a friend, which can guide our actions and emotions. A hexis is a characteristic, capacity or disposition that one ‘owns’; its etymology is the Greek word ekhein, the term for ownership. For Aristotle, a person’s character is ultimately a sum of their hexeis (plural).

An ethos, on the other hand, is what allows one to develop hexeis. It is both a way of life and the basic calibre of one’s personality. Ethos is what gives rise to the essential principles that help to guide moral and intellectual development. Honing hexeis out of an ethos thus takes both time and practice. This version of habit fits with the tenor of ancient Greek philosophy, which often emphasised the cultivation of virtue as a path to the ethical life.

Millennia later, in medieval Christian Europe, Aristotle’s hexis was Latinised into habitus. The translation tracks a shift away from the virtue ethics of the Ancients towards Christian morality, by which habit acquired distinctly divine connotations. In the middle ages, Christian ethics moved away from the idea of merely shaping one’s moral dispositions, and proceeded instead from the belief that ethical character was handed down by God. In this way, the desired habitus should become entwined with the exercise of Christian virtue.

The great theologian Thomas Aquinas saw habit as a vital component of spiritual life. According to his Summa Theologica (1265-1274), habitus involved a rational choice, and led the true believer to a sense of faithful freedom. By contrast, Aquinas used consuetudo to refer to the habits we acquire that inhibit this freedom: the irreligious, quotidian routines that do not actively engage with faith. Consuetudo signifies mere association and regularity, whereas habitus conveys sincere thoughtfulness and consciousness of God. Consuetudo is also where we derive the terms ‘custom’ and ‘costume’ – a lineage which suggests that the medievals considered habit to extend beyond single individuals.

For the Enlightenment philosopher David Hume, these ancient and medieval interpretations of habit were far too limiting. Hume conceived of habit via what it empowers and enables us to do as human beings. He came to the conclusion that habit is the ‘cement of the universe’, which all ‘operations of the mind … depend on’. For instance, we might throw a ball in the air and watch it rise and descend to Earth. By habit, we come to associate these actions and perceptions – the movement of our limb, the trajectory of the ball – in a way that eventually lets us grasp the relationship between cause and effect. Causality, for Hume, is little more than habitual association. Likewise language, music, relationships – any skills we use to transform experiences into something that’s useful are built from habits, he believed. Habits are thus crucial instruments that enable us to navigate the world and to understand the principles by which it operates. For Hume, habit is nothing less than the ‘great guide of human life’.

It’s clear that we ought to see habits as more than mere routines, tendencies and ticks. They encompass our identities and ethics; they teach us how to practise our faiths; if Hume is to believed, they do no less than bind the world together. Seeing habits in this new-yet-old way requires a certain conceptual and historical about-face, but this U-turn offers much more than shallow self-help. It should show us that the things we do every day aren’t just routines to be hacked, but windows through which we might glimpse who we truly are.