Let me begin with a true story. I once gave a talk at the Sociological Institute at Amsterdam University. A Dutch sociologist, Gerard de Vries, was deputed to comment on my talk. He said my picture of different theories about just one world was utterly naive: different theories, different worlds. He gave an example: "When the concept "person with an IQ two standard deviations above the mean" was invented new entities came into being". So, I replied, there are two ways of making babies, the way we all know and love, namely love, and this new way, psychological theorising. I was then told that the new entities were not babies, were not even persons with an IQ two standard deviations above the mean. I could form no clear idea of what kind of thing they were. My ex-friend Gerard de Vries was, of course, a conceptual idealist.