John Anderson’s philosophy is typically described as Realist by which it is typically meant that it was a systematic Realism. That is, his philosophy articulated a Realist interpretation of the traditional subjects of metaphysics, ethics, and aesthetics.
Anderson’s Realism was based on the doctrine of external relations which held that there is an absolute distinction between things in the world and the relations that they have, such that no thing can be constituted by the relations that it has. Further, this doctrine implied that the qualities that any object has cannot be constituted by the relations that the quality might have.
Such relations might be ordinary relations in space and time (spatio-temporal relations between objects) or may be particular relations such as knowing or perceiving which minds have towards objects.
On the basis of this view of relations, Anderson held that the subjects of metaphysics, ethics, and aesthetics – viz. truth, goodness, and beauty – could not be constituted by the relations that they have.