Ruth Millikan has hypothesised that human cognition contains ‘consistency testers’. Consistency testers check whether different judgements a thinker makes about the same subject matter agree or conflict. Millikan’s suggestion is that, where the same concept has been applied to the world via two routes, and the two judgements that result are found to be inconsistent, that makes the thinker less inclined to apply those concepts in those ways in the future. If human cognition does indeed include such a capacity, its (...) operation will be an important determinant of how people use concepts. It will have a major impact on which concepts they deploy and which means of application (conceptions) they rely on. Since consistency testers are a selection mechanism at the heart of conceptual thinking, they would be crucial to understanding how concepts are selected – why some are retained and proliferate and others die out. Hence, whether consistency testers for concepts exist, and how they operate, is an important question for those seeking to understand the cultural evolution of concepts, and of the words we use to express them. (shrink)