  Strawson (1979) argued that the primary system, that purporting to describe no more than what was ‘strictly available’ to perception, could only be described using concepts available to those already acquainted with the secondary system. A consequence of this, he claimed, was that the secondary system embodied in ordinary perceptual judgments could not be a theory with respect to which the primary system was the data – the data have to be describable in terms that do not presuppose the very theory for which they are the data.  Although, he argued, it may be possible, though difficult, for us to strip our vocabulary describing our experience of such secondary-system concepts, such an effort on our part would be unusual, and not at all like what is involved in our common-sense perceptual judgments, those that Ayer supposes to be the result of some theorizing on our part. For Strawson, our commitment to a conceptual scheme of a realist character is ‘something given with the given’ (Strawson 1979, p. 47).