I have appropriated the terms ‘descriptive’ and ‘revisionary’ metaphysics from P.F. Strawson's Individuals. In the Introduction to that work he draws a broad general distinction between two types of metaphysics. Descriptive metaphysics is concerned to ‘describe the actual structure of our thought about the world’ while revisionary metaphysics is ‘concerned to produce a better structure’. They also differ in that revisionary metaphysics requires justification of some sort whereas descriptive metaphysics does not. Strawson makes this point when he says, ‘Revisionary metaphysics is at the service of descriptive metaphysics’. Thus, the descriptivist has the sober, scientific task of elucidating our extant conceptual schema while the revisionist has the speculative, slightly literary job of inventing a new conceptual schema.

Do I ever directly raise my arm? Before dealing with this question we must make clear that the corresponding affirmation is to be taken as a way of rejecting one interpretation of the question, ‘In doing or by doing what do I raise my arm?’ On the interpretation of the question I have in mind the appropriate reply, if the question were not rejected, would be, ‘I raise my arm in or by doing something internal’. The way we are employing the phrase ‘doing something internal’ will, I think, become clear when we consider candidates for the description ‘doing something internal’. But it is important to remember that to affirm that I directly raise my arm is to reject the question, ‘In doing or by doing what do I raise my arm?’ on our interpretation of the question.

In ‘Scientific Materialism and the Identity Theory’ Malcolm argues that Smart's brain-mind identity theory is not even false, but is unintelligible. I want to comment on his arguments.

Psychological time—as distinct from physical time—divides the past from the future by means of the experienced present and serves as a frame of reference for objects, events, actions, and persons. There are cases when our understanding of objects and events gains in depth with every additional time dimension, until we are able to arrange all the data in a meaningful sequence ranging from the past through the present to the future across time. A description of city traffic when confined to the present is one step towards analysing special problems and understanding congestion in certain areas. The historical development of the city offers additional insight into the evolution of bottlenecks, while current changes, made by the municipal authorities, can only be understood in connection with a long-term development plan. A lecturer on town planning will, therefore, offer his audience a more profound understanding of the subject by combining a description of the visible present with a causal explanation of the past and a teleological account of future projects.