In the seventeenth century there was still no clear distinction between the child’s interiority and the adult’s, since ‘saving’ grace could arrive at any point in the lifespan. However, a rudimentary developmental idea was already defining the category of childhood more sharply by calendar age. This becomes clear in the principles behind the experimental primary schools established by the Jansenist wing of French Catholicism, including figures such as Antoine Arnauld and the Abbé de Saint-Cyran, as an alternative to Jesuit education. The Jansenist schools aimed at preserving the purity of children assumed to be elect (i.e. those of their own families) from contamination by the surrounding mass of reprobates in thrall to the Devil. The educational method was precisely not religious instruction but a secular, humanist curriculum based on reason. This went hand in hand with close control of the children in a panopticon; school discipline switched from physical punishment to moral shaming. The history of education as an academic discipline shows an unwitting bias towards being a history of the elect child.

The first principles behind the developmental idea are linear time, interiority and staged structure. ‘Development’ is one particular historical way of conceptualizing the primary principle of change; in it, human time is an attempt at successful ‘recapitulation’ (a term that would reappear with modern developmental psychology’s founder, G. Stanley Hall) of Adam’s initial failure. In monotheism, time constructs interiority as permanence, ‘the mind’, in contrast with the temporary visitations of pagan or shamanic religion. Medieval psychology saw a proliferation of its ‘faculties’ (memory, imagination, judgement) and ‘operations’ (abstraction, attention, consciousness, logical reasoning, information-processing), which penetrated both the monastic and the humanist idea of the individual. Augustine’s ‘six ages’ of man gave the lifespan a fixed structure. Following the Reformation, change in the elect minority was seen either as instantaneous or as a stadial sequence: Jansenists and Calvinists on the one hand, Jesuits and Arminians on the other, disputed the function of human agency in relation to divine determinism.

The normalization of the elect acquired a corresponding theoretical framework. From the late seventeenth century the preferred explanation for physical growth had been ‘preformation’: the theory, starting with Swammerdam, that all living organisms have pre-existed from the Creation and are born as miniature versions which ‘unfold’ through predetermined stages. Leibniz suggested applying preformationism to the human mind. It was in this context that the word itself, ‘development’ (whose first appearances are better translated as ‘unfolding’), was first employed. The pioneering naturalist Charles Bonnet went on to apply the theory of preformationism to what he now expressly termed ‘psychology’. He identified psychology with the stages of regeneration in the elect (the so-called economy of grace); he linked this development of the person to the Enlightenment idea of ‘social progress’, and represented both as a gradual (rather than instantaneous) unfolding of biblical Revelation.

Psychological development is not something self-evidently natural but a partly human creation, emerging contingently from the midstream of human history. Modern developmental psychology is a continuing outgrowth of the religious outlook. Christian ways of thinking have become psychological ones, and they share a common underlying metaphysic; philosophers writing about time such as Heidegger and Ricoeur spring from this same tradition. The so-called predestination of souls from before birth (saved or damned) by divine determinism transitioned into pre-natal biological determinism of cognitive ability and disability. The theory of developmental stages – today (for example) the arrival of ‘logical reasoning’ or ‘empathy’ in the child – emerged from theories about the arrival of saving grace in the individual.

When influential philosophers prior to the Enlightenment such as Leibniz and Malebranche speculate about the interior life of ‘Man’ they presuppose the elect, saved man. This continues to be the case with Pierre Nicole and Jacques-Joseph Duguet, whose writings coincide with Jansenism’s turn towards a movement of political opposition to absolutism that ended up in Jacobinism. The shadows cast by predestination can still be detected even in Locke and Montesquieu, regarded as the founding figures of the Enlightenment. The theory of election would retain a subliminal presence in the history of the human sciences of the eighteenth century. So too would their increasing preoccupation with causality in psychological and social identity; out of the causes for election and reprobation came the imputation of causes for developmental normality and abnormality (‘idiocy’, ‘imbecility’ etc.) in the history of medicine.

Blaise Pascal’s Pensées hint at a temporal description of soul and mind, and were deeply influential upon subsequent pioneers of the developmental idea. On the one hand, using spatial analogies drawn from geometry, Pascal considered the most important aspect of the individual’s interiority to be ‘Order’. On the other, Order was a temporal phenomenon because it had to manage the movements of interiority over time, which otherwise had a ‘lunatic’ unpredictability. The political theory of absolutism, which Pascal approved, arose in order to control this. Pascal believed it was possible even for the predestined elect to lapse or degenerate, and initiated the focus on time as a ‘counterweight’, a way of pushing back against this. His account of the power of the individual will in relation to God’s operation of that will marks the start of a resemblance to the account of ‘nature versus nurture’ in modern psychobiology.

The application of the word ‘development’ to a fully formulated principle of temporal Order becomes ubiquitous in Rousseau’s Emile. The biologist Buffon, the psychologist Condillac and particularly Bonnet all influenced this seminal treatise. But where they had written of development only occasionally and in an abstract sense, with Rousseau it becomes normative and the main descriptor of the structured lifespan of the individual. Rousseau retains the older sense of development as the ‘unfolding’ of an already existing, preformed structure; nevertheless, he also reveals in outline the modern human sciences’ presupposition that the child is an incomplete being. Thanks to Bayle and Diderot, Rousseau derived his concept of a political General Will, irrespective of the individual will, from that of God’s general will to save humankind that does not take individual behaviours into account; this has its psychological equivalent in Rousseau’s creation of ‘the abstract man’, against whose developmental norms the individual must be measured.

The previous themes reach into modern debates about freedom and necessity, which are still central in education and psychology today. Contributing to the rise of formal disciplines of developmental and child psychology, educational psychology, clinical psychology and cognitive psychology, as well as psychiatry, empirical approaches based on sense perception began in the mid-eighteenth century; but they are equally the outcome of broader religious and cultural influences. The book therefore concludes with an overview of the direct traces on the modern disciplines of the religious ideas discussed in earlier chapters: in Britain through David Hartley, Joseph Priestley and Francis Galton, and the nature-versus-nurture formula; and in France Hippolyte Taine, Alfred Binet (creator of the ‘mental age’ score, subsequently IQ measurement) and Jean Piaget himself.

Development is one of psychology’s given components. Psychologists and consequently the lay public in Western cultures see childhood as well as adult character in terms of what I call here ‘the developmental idea’, describing a scientific category that exists ‘out there’ in nature. The human interior, it seems, passes through a necessary series of stages that play out over time. And so the youngest of us are only potential human beings; we do not start to display signs of ‘empathy’, say, until we are three, or ‘logical reasoning’ until we are six: or so we are told. Adult character and conduct are the desired outcome of those stages (though a few of us, it appears, never reach them even when we arrive at adulthood by calendar age).

The themes from this book require extending into other research areas. First, the history of political thought and ideas: psychology itself is an idea, since modern political thought emanated not only from thinking about ‘man’ but also from what the thinker believed himself to be, qua man: that is, his interior religious and/or psychological status. Second is the history of education, where the importance of the German-language tradition (Schleiermacher, Herbart, Froebel) might lead to studying the idea of universal salvation as a founding discourse of modern schooling, and the ‘developer’ as the individual embodiment of social and national progress. Third comes disability history, concerning institutions and asylums, which has encouraged a single reified notion of developmental disability; a critical conceptual history should make it possible to stand outside this. The fourth area is literature. The novel is the classic literary ‘form’ of a linear developmental narrative, but its historical examples reveal it to be a constant subversion rather than reflection of the developmental idea, even in the typical novel of personal formation (Bildungsroman).