On Choice of Time Metric. What criteria ought to be satisfied by those observable processes which, accompanied by a function assigning values to intervals of that processes, serve as the standard for measurement of time? In how far do the criteria which can reasonably be established admit of an unambigous definition of time metric? That are the questions to which I have addressed myself in the paper. Peter Janich has aimed at solving the problem with careful avoidance of any reference (...) to physical theory. Although this paper owes a great deal to his ‘Protophysik der Zeit’, reasons will be ad-vanced that it is in principle impossible to give a foundation of time metric without any reference to physical theory. It follows that taking results of physical theory into account is unavoidable as far as a definite decision concerning the choice of time metric is aspired. At first sight reference to law-like assertions on the duration of temporal intervals appears to be paradoxical for it means to take something which originally ought to be submitted to experimental test as the standard for measurement. Poincaré is fairly conscious of this problem, yet explicitly acknowledges that there is a mutual relationship between definition of time metric and physical theory. It will be shown that this kind of mutual relationship which even might be termed as circular does not void physical theory of empirical content. Thus in the final part I am concerned to free the position which recommends reference to physical theory from its paradoxical image in order to advance a conventionalist account as a sceptical, but nevertheless fully satisfying solution. (shrink)