POSITIVISM IN THE NATURAL SCIENCES 75 Schrodingcr's wave equation. This is a causal change described in terms of differential equations and does not differ in quality from the change of the state of a macroscopic system. The characteristic feature of quantum mechanics, however, arises in the observation of such a microscopic system; a measurement of the same physical quantity in the same state, does not always yield a definite icsult and we can only predict statistically a probability for getting a specific result. Moreover, the state of the system or the wave function changes discontinuously and noncausally through the measurement; thus which state the system changes to, depends on the measured result of the physical quantity. The essential point of the ^observation problem" is to clarify the relation of these two changes that is the continuous and causal change of the state of a closed system-and discontinuous and non-causal one which asises in the measurement of the system. Now consider the characteristic feature of a measuring picccss. An obseivation is an action on ^an object" with the "measuring apparatus" to measure quantities concerning the former, for example, reading a change of the scale appearing in the latter. Then in Quantum Mechanics even if the combined system of two is, as a whole, in a pure quantum mechanical state, it can be proved that as for the subsystem, it is generally no longer in a pure state, but consists of a statistical mixture of a number of quantum mechanical states. This is a characteristic of quantum mechanics and indicates a dialectical relationship between the part and the whole, and between the contingency and necessity, which can neier be understood by formal logic alone. The discontinuous and non-causal change whicH arises in the measuring process contrary to the continuous and causal change of the state of the closed system is a consequence of such an objective ^quantum mechanical law of combination" between ^object" and ^measuring apparatus," and has nothing to do with the so-called ^action of the subject on the object." The statement which has hitherto been frequently made that quantum mechanics ^rejects" the objective reality of externality is based on a wrong understanding of the observation problem. The statistical nature of quantum mechanical measurement is a consequence of a ^material interaction" between the ^object" and the ^measuring apparatus" both of which have an "objective existence," and that statistical nature is not due to the action of the subject on this object. Quantum mechanics is statistical in the part, that is, in the pheno-' menon, being founded by the state of the system as a whole that obeys the causality in the strict sense. Heisenberg's uncertainty principle indicates the limit in each observation, but never the limit of recognition. But observation is not recognition. Recognition is the copying of nature. It is however not. a dead static reflection like an image in a mirror. On the contrary, our recognition penetrates deep into and still deeper into the essence of nature. And from the historical point of view, it is the process of bring-