There can be no knowledge without sensation, but sense data cannot alone provide knowledge either. Knowledge is possible because it is about how things appear to us, not about how things are in themselves. Reason provides the structure or form of what we know, the senses provide the content. Perhaps there is nothing about knowledge that is ultimate, but rather a web of interlocking beliefs. Justification is thus a social, historical phenomenon.
Abnormal discourse lacks such criteria.
Periods of social change are characterized by struggles between normal and abnormal discourse. Truth is thus a property of a statement. The facts exist independently of our knowledge of them. Accurate observations can report actual states of affairs and cannot result in reasonable disagreement. This changes the notion of truth away from a property of a statement to the reasons we provide for beliefs.