ABSTRACT
The modern concept of nature, of the physical, was determined by the introduction, early in the seventeenth century, of the concept of matter as substance. This entailed an ontological dualism which has ruled thought down to the present day. In this doctrine physical existence was conceived as material, implying the exclusion from the physical existent of anything of the kind of perception, thought, feeling, emotion, etc., all of which were relegated to an ontologically separate existent or substance. Even when the doctrine of material substance was rejected, as by Leibniz, the influence of the ontological dualism was determinative; for Leibniz and other opponents of materialism conceived substance by contrast with that doctrine as 'spiritual' or 'mental'. This is true not only of the seventeenth century but of thought down into this century, a good instance of this being the 'pan-psychism' of Peirce, Whitehead, and other thinkers. In the early part of the present century the theory of 'neutral monism' gained some prominence, but it too was determined by the dualism inherited from the seventeenth century, for in this theory substance was conceived as neither material nor mental, but neutral to both, from which they arise.
