>>13217990A similar discussion could be given on the a priori character of space and time as forms of
intuition. The result would be the same. The a priori concepts which Kant considered an
undisputable truth are no longer contained in the scientific system of modern physics.
Still they form an essential part of this system in a somewhat different sense. In the discussionof the Copenhagen interpretation of quantum theory it has been emphasized that we use the
classical concepts in describing our experimental equipment and more generally in describing that
part of the world which does not belong to the object of the experiment. The use of these
concepts, including space, time and causality, is in fact the condition for observing atomic events
and is, in this sense of the word, `a priori.' What Kant had not foreseen was that these a priori
concepts can be the conditions for science and at the same time can have only a limited range of
applicability. When we make an experiment we have to assume a causal chain of events that
leads from the atomic event through the apparatus finally to the eye of the observer; if this
causal chain was not assumed, nothing could be known about the atomic event. Still we must
keep in mind that classical physics and causality have only a limited range of applicability. It was
the fundamental paradox of quantum theory that could not be foreseen by Kant. Modern physics
has changed Kant ' s statement about the possibility of synthetic judgments a priori from a
metaphysical one into a practical one. The synthetic judgments a priori thereby have the
character of a relative truth.
If one reinterprets the Kantian `a priori' in this way, there is no reason to consider the
perceptions rather than the things as given. Just as in classical physics, we can speak about
those events that are not observed in the same manner as about those that are observed.
Therefore, practical realism is a natural part of the reinterpretation.
