The subtitle to the Principles and two interlocutors

Berkeley’s Principles, and the immaterialist philosophy it embodies, has a number of definite aims. The general tenor of them is evident from its subtitle, which, as we noted, is ‘wherein the Chief Causes of Error and Difficulty in the Sciences, with the grounds of Scepticism, Atheism, and Irreligion, are inquired into’. Berkeley sees the dangers of scepticism, atheism and irreligion as stemming from philosophical sources, rather than a threat stemming from ordinary common sense. The philosophy with which he is concerned is the then relatively new ‘mechanical philosophy’, an immensely subtle and complex world view associated with the ‘scientific revolution’, the crowning achievement of which was the work of Isaac Newton.

A pioneer in this new philosophy was René Descartes (1596–1650). For him, the ultimate nature of the material world is knowable to humans and it consists of extended things in motion. All else that we seem to perceive – colours, tastes, smells, etc. – are best understood in terms of the effects of matter in motion on minds. As Richard Westfall puts it in a now classic study ‘bodies comprise only particles of matter in motion, and all their apparent qualities (extension alone excluded) are merely sensations excited by bodies in motion … The world is a machine, composed of inert bodies, moved by physical necessity, indifferent to the existence of thinking beings.’ This austere view of the world was driven by a new conception of science, which, very roughly, aspired to explain the behaviour of the physical world by appealing to as few a number of properties as possible. Descartes contrasts this aspiration with ‘scholastic philosophy’, which he is keen to reject as explanatorily bankrupt in its constant appeal to numerous ‘qualities’ or ‘forms’ to ‘explain’ observable phenomena, themselves stand in need of explanation. Thus, he writes: