To illustrate his point, he [Max Weber] asks us to suppose that psychology has advanced so far that it is possible to assess the precise neurological causes behind the reasoning of a mathematical theorem; that never suffices to determine whether or not that theorem is true .... Why? Because there is a fundamental distinction in principle between determining causes and assessing validity, which no amount of causal explanation will ever surmount. (Beiser, p. 542)I thought this was Frege's anti-psychologism. But I've just looked at a paper by R. Lanier Anderson, who, in the course of tracing anti-psychologism's neo-Kantian roots, distinguishes between two kinds of anti-psychologism. Anderson credits Lotze and Windelband with developing the above variety, which he contrasts with Frege's. Anderson says:
The earliest clear occurrence I have found of "psychologism" in the now familiar pejorative sense is Windelband’s "Kritische oder genetische Methode?" published in Präludien (1884). But even though the word "Psychologismus" was not common before the 1880s, the basic ideas behind the charge of a psychologistic fallacy became increasingly widespread through the 1870s. One of the most widely influential early sources for the emerging antipsychologistic camp was the 1874 Logik by Windelband’s teacher, Hermann Lotze. (Anderson, "Neo-Kantianism and the Roots of Anti-Psychologism," British Journal for the History of Philosophy, 13:2 : 287-323 [at 293-4])Here's how Anderson characterizes Frege's anti-psychologism:
Frege makes it a "fundamental principle . . . always to separate sharply the psychological from the logical, the subjective from the objective" ... and he famously quips that "number is no whit more an object of psychology or a product of mental processes than, let us say, the North Sea is" .... Frege does sometimes insist that logical laws, unlike psychological laws, serve as a normative standard for thinking, but for him, that point always depends on a more fundamental claim that logic treats objective, mind-independent laws of an abstract character, not facts about the subjective psychology of reasoners. (Anderson, p. 295)A similar anti-psychologistic point may be made in connection with ethics. E.g., here's H. Allen Orr in a review of one of E. O. Wilson's books:
When Wilson "predicts," for example, that ethical phenomena will also turn out to be neural, it's unclear what interesting conclusion he thinks follows from this fact. Have we here "reduced" ethics to biology? Anyone who's tempted to answer yes should consider one further "prediction": Mathematical thoughts will also involve neurons. You're free, of course, to conclude that ethical truths are just biology but only at the considerable risk of arriving at the same conclusion about "2 + 2 = 4". (H. Allen Orr, 'The Big Picture', review of E. O. Wilson's Consilience, Boston Review, Oct/Nov, 1998)One sees variations on these anti-psychologistic points in Massimo Pigliucci's and Bill Vallicella's objections to Lawrence Krauss's latest bit of a priori dogmatizing.