 Although the arguments from productivity and systematicity are usually alluded to in the same breath, they are very different considerations. Unlike the main premise of the former, the main premise of the latter is anything but obvious. Particular instances are plausible enough: it seems reasonable that anyone who can understand ‘The dog is asleep’ and ‘The cat is awake’ can also understand ‘The dog is awake’ and ‘The cat is asleep’, and that anyone who can understand ‘black dog’ and ‘white cat’ can also understand ‘black cat’ and ‘white dog’. But do all who understand ‘within an hour’ and ‘without a watch’ also understand ‘within a watch’ and ‘without an hour’? And do all who understand ‘halfway closed’ and ‘firmly believed’ also understand ‘halfway believed’ and ‘firmly closed’? As Johnson (2004) argues, the claim that natural languages are systematic presupposes a natural non-overlapping linguistic categorization of all the expressions. The existence of such a categorization is a bold empirical hypothesis.