Dear Mohan, I suppose that for Hume the idea of a collie is a complex idea, but whether it is a complex of ideas of simpler spatial parts or some other sort of complex, say of an animal of a certain sort, depends on whether it is as you say a visual idea, the idea of the look of a collie, or not. Hume certainly needs ideas which are not copies of any sense impression or complex of them. The idea of an idea, for example, or the idea of inference, or of thinking. I have just given a talk at the AAS conference in Sydney defending Hume against conceptualists like McDowell (who was there, and unconvinced.) Thanks, Annette