The Criteria of Proof

Abstract

Knowledge, we have seen, may concern events immediately given to consciousness and it may also concern things which are perhaps never data of immediate experience. Which of these forms of knowledge can be considered capable of proof, then? The question of proof is particularly difficult when we admit the equal validity and exclusive insufficiency of two diametrically opposing premisses which never entail propositions concerning each other. The ‘knowledge’ of the sceptic in many cases is not even a part of the knowledge of the realist (for if they explain the very same things, they explain them differently) and the ‘knowledge’ of the realist is exposed to grave doubts from the viewpoint of the sceptic. If order is to be made in this extremely difficult situation, we have to introduce criteria for the definition of proof, which are to determine just what we can hold to be veridical knowledge. These criteria have to be extraneous to the investigations themselves, and be clearly established before investigations are being undertaken. As Ayer resumes his conclusions in this respect, “the necessary and sufficient conditions for knowing that something is the case are first that what one is said to know be true, secondly that one be sure of it, and thirdly that one should have the right to be sure. This right may be earned in various ways; but even if one could give a complete description of them it would be a mistake to try to build it into the definition of knowledge, just as it would be a mistake to try to incorporate our actual standards of goodness into a definition of good.” ¹ Now it is evident that both the sceptic and the realist know that what they say is the case, and that they may even be sure of it. But it is equally evident that unless we espouse their particular root-axiom, we shall not admit that they have the right to be sure. It follows that the adoption of the root-axiom is not determined by the arguments proposed on their basis, but must be decided previously. Hence, we need criteria of proof which will let us decide in which context to opt for ‘consciousness’ and in which for ‘being’ as basic premiss. But, since neither ‘consciousness’ nor ‘being’ are sufficient in themselves for an impartial investigation of the nature of reality, we require criteria for choosing both consciousness and being as root-axiom, and a method for testing the validity of the contradictions that would normally result in arguments from them. In addition we must have a criterion to prevent the accumulation of redundant principles. Some of the criteria must function for choosing the premisses, others for checking the inferences.