 For example a panic on the stock exchange can be most conveniently analysed by attempting to determine first what the course of action would have been if it had not been influenced by irrational affects; it is then possible to introduce the irrational components as accounting for the observed deviations from this hypothetical course...Only in this way is it possible to assess the causal significance of irrational factors as accounting for the deviation of this type.The construction of a purely rational course of action in such cases serves the sociologist as a type (ideal type) which has the merit of clear understandability and lack of ambiguity.By comparison with this it is possible to understand the ways in which actual action is influenced by irrational factors of all sorts, such as affects and errors, in that they account for the deviation from the line of conduct which would be expected on hypothesis that the action were purely rational.