 At the turn of the twentieth century, the relation between philosophy and psychology was a topic of intense debate in various academic circles. Among other issues, this debate concerned whether psychology should be understood as a philosophical discipline or, the other way around, whether philosophy should be grounded in psychology. Of particular importance to this debate is whether ethical, metaphysical and logical concepts are psychological or not. Since these concepts are usually held to be constitutive of the corresponding laws of ethics, metaphysics, and logic, claiming that these concepts are psychological would imply that the nature of such laws is psychological and, thus, that their investigation is a task that should be assigned to psychology. To give an example, according to logical psychologism (Mohanty 1982: §2; Kusch 2007 [2011]), the law of the excluded middle is about the psychological impossibility of a subject judging that p and that non-p at the same time. On this interpretation, this law is psychological in nature and its investigation should be pursued by psychology. Psychologism was not uncontested, as we will see: although the anti-psychologist camp encompassed different views as to how logical, ethical, and metaphysical concepts have to be positively defined, these views all agreed on the negative insight that logic, ethics, and metaphysics do not depend on psychology.