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.