Since knowledge is always knowledge of regularities and has therefore to be couched in terms of universal laws, it follows that knowledge cannot be representational. Knowledge is neither a map nor a mirror nor a portrait. Once this is admitted, we can again see the historical element in knowledge. If knowledge is knowledge of general laws, then the growth of knowledge is not just an accumulation of detailed and particular observations, but a growth of the universality of the general laws. We speak of progress, when the particular facts explained by a general law can be explained by a new general law which explains not only the particular facts already explained, but also other particular facts which had not been explained by an old general law. Knowledge of regularities cannot be representational because a universal law does not represent anything we can observe. At best, we can observe only a limited number of instances. A general law asserts something about regularities and therefore cannot represent what we can observe. With this argument we can eliminate from consideration all those thorny problems which occupied Positivists in general and Mach in particular. Mach was deeply concerned to distinguish between presentationalism, of which he approved, and representationalism, of which he disapproved. The former was the idea that the world is presented directly to consciousness and that the appearances are the external world and that observation of particular instances is real knowledge. Statements of regularities, he said, are merely short hand devises to sum up myriads of direct observations. Representationalism, on the other hand, was the idea that the external world is not directly presented to consciousness and that appearances are something mental and that the external world is something one can reliably infer from these appearances. If one take this view, there is no reason, he said, why one should imagine that any inference of this kind is ‘reliable’. Since we cannot consider either presentationalism or representationalism as knowledge, the whole question as to which of these two views is the correct one is without interest"
From Knowledge of the Growth of Knowledge, page 26
