Sentences like 'Joe desires a unicorn' can be paraphrased as 'Joe desires-true of himself "possesses a unicorn"', eliminating the need for the intentional object to exist.

Thinking very much in causal terms about beliefs and desires fits in very well not only with folk psychology but also with Humean ideas about the motives of action. Though this point of view has been criticised by some philosophers it does seem to be right, as can be seen if we consider a possible robot aeroplane designed to find its way from Melbourne to Sydney. The designer would have to include an electronic version of something like a map of south-eastern Australia. This would provide the ‘b