Halliday & Matthiessen (1999: 68):
Categorisation is often thought of as a process of classifying together phenomena that are inherently alike, the classes being as it were given to us by the nature of the experience itself. But this is not what really happens. Categorising is a creative act: it transforms our experience into meaning, and this means imposing a categorical order rather than putting labels on an order that is already there. As Ellis has expressed it, categorisation consists in grouping together sets of phenomena that are essentially not alike (1993: Ch. 3). There would be indefinitely many ways of construing analogies among different elements in the total flux of experience; what our semantic resources enable us to do is to construe those analogies which yield categories resonating with what as a species, and as members of a particular culture, we have found to carry material and symbolic value.