1. Introduction. The idea of “indeterminacy”—
often also called loosely “uncertainty”—is widely used
in physics and is of particular importance for quantum
mechanics, but has rarely, if ever, been given a strict
explicit definition. As a consequence it is used in at
least three different, though related, meanings which
will be sharply distinguished in the present article. (a)
It may denote any type of acausal (accidental, contin-
gent, indeterministic) behavior of physical processes,
usually in the realm of microphenomena, implying
thereby a total or partial breakdown of the principle
of causality; (b) it may denote any type of unpredict-
able behavior of such processes without necessarily
involving a renunciation of metaphysical causality; (c)
it may denote an essential limitation or imprecision of
measurement procedures for reasons to be specified by
a concomitant theory of measurement.
To avoid ambiguities we shall in what follows call
indeterminacy if used in the sense (a), acausal indeter-
minacy or briefly a-indeterminacy; if used in the sense
(b), u-indeterminacy; and if used in the sense (c),
i-indeterminacy. Clearly, a-indeterminacy implies, but
is not implied by, u-indeterminacy, and does not imply,
nor is implied by, i-indeterminacy; neither do the other
two imply their partners. If however predictability is
understood to refer exclusively to sharp values of
measurement results, i-indeterminacy implies u-inde-
terminacy. Furthermore, the validity of these concepts
may depend on the domain in which they are applied.
Thus a- or u-indeterminacies may be valid in micro-
physics but not in macrophysics.
