This paper offers a general analysis of what it means to say that a representation or concept is 'abstract', and then applies the analysis in two specific areas, namely colour terms research and phonological theory. Starting from acceptance of the widely agreed proposition that cognition involves categorisation of reality via mediating concepts, it follows the implications of this idea in metatheoretical analysis of the terms and concepts used in theories about colour terms and phonology. In relation to colour terms, this analysis gives a way of understanding, and resolving, a debate sparked by Lucy (1997) about the use of the Munsell colour chart as the basis of crosslinguistic data collection in this area. In relation to phonological theory, analogous arguments call into question some fundamental tenets of phonological theory, for example the idea that a phonological representation is more abstract than a phonetic representation. The possibility of changing these tenets, and the consequences for both theoretical and applied phonology, are explored in detail.