 Broad distinguishes two chief aspects of philosophical thinking. He labels these critical philosophy and speculative philosophy. Critical philosophy has two chief tasks, one of which is to analyse “certain very general concepts such as number, thing, quality, change, cause, etc.” (1924, p. 82). We make use of these and a whole host of other concepts in science and ordinary life. Although we are typically able to apply them fairly consistently, we are not able to analyse them. Nor are we able to state their precise relations to each other. One task of critical philosophy is to provide analyses of such concepts. It becomes evident that this is an important task as soon as it is realized that when we seek to apply these concepts to odd or exceptional cases we are often uncertain whether they are applicable. For example, it might be unclear whether a certain individual with a multiple personality disorder is a person or  not.[14]  Such difficulties arise because “we are not clear as to what we mean by ‘being a person’” (1924, p. 83). There is, therefore, a need for an intellectual discipline that seeks to analyse and define this and many other concepts.