218 COLLECTIVE REVIEWS
respect, medical men must accustom themselves to a new mode of thought, a mode of thought which corresponds more closely to reality and which demands the presence of conviction as regards the truth of its content: a new discipline of thought must be brought into play. It is not scientific thought which constitutes the opposite of ordinary thought with its mixture of autistic and realistic, of attentive and of negligent procedure; since the mer- chant, the industrial manager, etc., no less than the scientist, have to think in accordance with the strictest logic; scientific thought too, where it approaches new territory, is related to autistic thin- king. 'Exact thought' also is only a relative concept. Exactness of thought is shown not so much by quantitative measurement and the production of figures as by the correct appUcation of the laws of thought, the accurate observation of facts, the constant reference to reality, the avoidance of ambiguities, the stem realisa- tion of all presuppositions that are employed; all this, in its tota- lity, may be called disciplined thought.
Among the weapons of disciplined thought is to be reckoned probability, which should be an attribute of every judgement. In the case of facts newly discovered by science, it is not possible to determine probability in the mathematical sense, since not all the relevant facts and influences can be known. When confronted with new discoveries, disciplined thought must therefore operate with probability factors which do not admit of exact mathematical expression but which nevertheless permit of an evaluation of the importance of each item.
But is this disciplined thought really possible in psychology? Bleuler shows that there is here no difference in principle between psychology and exact natural science. Jiisper's distinction between causal thought in natural science and understanding thought in psychology cannot be accepted without further discussion, since psychological motives are causal in exactly the same sense as are physical causes. Any apparent difference as regards causation in psychology is largely due to the fact that in this science it often happens that connections have to be studied within the limits of a single case.
But even a single case can be referred to previous experiences, as is actually done in psycho-analysis. Sympathetic insight into other minds, the similarity of mental process, the increased proba- liility of a connection in the case of two events both of which
