One vicious circle has appeared already in our introductory discussions, when we attempted to find an absolute distinction between physical and non-physical phenomena. The tests for physicality resolved themselves into ones for 'physical interaction, with physical bodies, and public to physical people suitably placed in the physical world'.l In practice this circularity causes no trouble. For we can proceed, in our tests, by successive stages from the obviously physical to the less obviously physical, judging the one by the other. The first stage, that is, the obviously physical, is judged tobe so by 'pure commonsense', which provides for us a broad recognition of different 'systems of behaviour', physical or non-physical.