The ascendancy of French political power supported literary success and scientific achievement. Investigators such as Lagrange, Laplace, and Lavoisier gave mathematical and empirical support to modern chemistry, physics, and biology. In parallel, philosophical discourses on psychology led to a reinterpretation of Descartes’ formulation to focus on sensation. Condillac, Bonnet, and La Mettrie argued for the equation of mental operations and sensory input, with the result that they reduced psychology to sensation. Helvétius and Cabanis attempted to back off from such extremism by asserting the mediating role of a central ego, although both remained committed to sensory physiology. Biran and Comte recognized the consequences of reducing psychology to mere sensory physiology, but each worked out separate solutions. Biran rejected sensationalism as inadequate, suggesting an individual psychology based on consciousness and the will. In contrast Comte ultimately accepted sensationalism and dismissed psychology. For him, the individual person should properly be studied by physiology; the individual behaving in a group is the province of sociology. Comte, however, advocated a spirit of objective observation that was eventually useful to psychology. Thus, the successors to Descartes in France left psychology in a somewhat tenuous position, removed from recognition as a formal discipline.

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.