When we say we ‘cannot see the wood for the trees’, we are expressing a need to establish a general picture of something that is more than the sum of its parts. Categorising and classifying things we encounter in everyday life are therefore important steps in the process of imposing some kind of order on the infinite varieties of human experience: they are part of a general strategy of ‘making sense of the world’ by artificially reducing variation to manageable proportions. For example, it is both conceptually and communicatively more economical if we can classify tulips, roses and daffodils as members of the general category flower or Volkswagens, Rovers and Nissans as belonging to the category car (or automobile).