 Already by the late 17th century the word ‘model’ could mean an object that shows the form, not of real-world objects, but of mathematical constructs. Leibniz boasted that he didn’t need models in order to do mathematics. Other mathematicians were happy to use plaster or metal models of interesting surfaces. The models of model theory first appeared as abstract versions of this kind of model, with theories in place of the defining equation of a surface. On the other hand one could stay with real-world objects but show their form through a theory rather than a physical copy in hand; ‘modelling’ is building such a theory.