In Kant, knowledge a priori means knowledge that we possess prior to sense-observation; and knowledge a posteriori means knowledge we possess posterior to sense-observation, or after observation; and I will use the terms a priori and a posteriori only in this temporal or historical sense. (Kant himself uses his term a priori to mean, in addition, knowledge that is not merely prior to observation but also `a priori valid; by which lie means necessarily or certainly true. Of course, I shall not follow him in this since I am stressing the uncertain and conjectural character of our knowledge.) So I shall use the term a priori to characterize that kind of knowledge - of fallible or conjectural knowledge - which an organism has prior to sense experience; roughly speaking, it is inborn knowledge. And I shall use the term a posteriori for knowledge that is obtained with the help of the sensitivity of the organism to momentary changes in the state of its environment. Using this Kantian terminology with the modifications I have just indicated, we can now say that Kants own position - highly revolutionary at the time - is this. Most knowledge of detail, of the momentary state of our surroundings, is a posteriori. But such a posteriori knowledge is impossible without a priori knowledge that we somehow must possess before we can acquire observational or a posteriori knowledge: without it, what our senses tell us can make no sense. We must establish an overall frame of reference, or else there will be no context available to make sense of our sensations. This a priori knowledge contains, especially, knowledge of the structure of space and time (of space and time relations), and of causality (of causal relations). I think that, in all these points, Kant is right. (Incidentally, I also think that he had hardly a real successor in this except perhaps Schopenhauer.) In my opinion, Kant anticipated the most important results of the evolutionary theory of knowledge. But I am going much further than Kant. I think that, say, 99 per cent of the knowledge of all organisms is inborn and incorporated in our biochemical constitution. And I think that 99 per cent of the knowledge taken by Kant to be a posteriori and to be data that are given to us through our senses is, in fact, not a posteriori, but a priori. For our senses can serve us (as Kant himself saw) only with yes-and-no answers to our own questions; questions that we conceive, and ask, a priori; and questions that sometimes are very elaborate. Moreover, even the yes-and-no answers of the senses have to be interpreted by us - interpreted in the light of our a priori preconceived ideas. And, of course, they are often misinterpreted. Thus, all our knowledge is hypothetical. It is an adaptation to a partly unknown environment. It is often successful and often unsuccessful, the result of anticipatory trials and of unavoidable errors, and of error elimination. Some of the errors that have entered the inheritable constitution of an organism are eliminated by eliminating their bearer; that is, the individual organism. But some errors escape, and this is one reason why we are all fallible: our adaptation to the environment is never optimal, and it is always imperfect. A frog is constituted a priori so that it can see its prey - a fly only when the fly moves. When the fly sits still, the frog cannot see it, even if it is very close: the frogs adaptation is imperfect. Karl Popper, All Life is Problem Solving.
Posted on: Sun, 23 Nov 2014 08:49:00 +0000
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