I want to begin with a discussion of De Emendatione. There is an obvious comparison between this and Descartes's Discourse on Method; and obvious contrasts. It does not look as though Spinoza's essay was written deliberately as an ‘anti-Discourse’. But many of the positions he criticises are reminiscent of Descartes and the contrasts are constructive. I shall use them to help highlight what is distinctive about Spinoza's position.

Notice first the way in which De Emendatione begins. The goal is to try to find out whether there was anything which would be the true good, capable of communicating itself and which alone would affect the mind. Compare the opening pages with the title ‘The Ethics’. Spinoza's aim is to see how to achieve ‘blessedness’. Note how this is immediately linked with questions concerning the understanding, its ‘purification’ and ‘improvement’. This is because it is not obvious what ‘blessedness’, ‘felicity’, ‘happiness’ and so on, consist in or how they are to be achieved.

Spinoza's starting point is that to answer these questions we have to understand what the nature of man is – because ‘the terms good and evil are applied only relatively, so that the same thing may be called both good and bad, according to the relations in view, in the same way as it may be called perfect or imperfect’. So we have to ask what is good in relation to man; and to answer this we have to understand the nature of this relatum– man. Moreover, we shall be asking what sort of relation between a man and the world around him is to be counted ‘good for him’. So the enquiry broadens into a general metaphysical one: into the nature of the ‘world’ and of man's ‘place’ in it.

Furthermore, since all this is something we are trying to understand, we must enquire into what counts as ‘understanding’ as far as men are concerned. Putting it another way, if we are to ‘purify’ and ‘improve’ the understanding, we have first got to understand what understanding consists in. Suppose an engineer is given a piece of machinery and asked to consider how it may be improved.