The problem that Husserl recognizes is: when our “faith in ‘absolute’ reason, through which the world has its meaning, the faith in the meaning of history, of humanity, the faith in [human] freedom, that is, [our] capacity to secure rational meaning for [our] individual and common human existence” is lost, the descent into skepticism is inevitable (Crisis, § 5, 13). The problem of skepticism is not some academic preoccupation of a lonely philosopher but has real repercussions for everyday living. If reason—this touchstone of truth—is relativized, all reasoning becomes suspect. By extension, if reasoning cannot provide justification for our claims about the world, human existence seems to be without any rational basis. It becomes meaningless.32 As Husserl notes in his last work, if the idea of reason is eliminated as superfluous because it is conflated with reasoning about facts, then society is in crisis because it lacks a firm foundation. To avoid such grave consequences, Husserl strives to elucidate the confusion of our age, “a collapse of the belief in ‘reason,’ understood [by] the ancients” as epistēmē (Crisis, § 5, 12). His struggle is against the substitution of epistēmē with doxa: changeable opinions that are presented without reasons to support them.
Husserl starts with psychological investigations in Philosophy of Arithmetic, only to become dissatisfied with the smuggling of psychological explanation into the system of formal knowledge, and thus opening a door to skepticism and relativism. As he says later, logic reduced to psychology becomes “a psychologistically determined technology of correct thinking.”33 Husserl realizes that by using a psychological type of explanation, “an unnoticed μετάβασις εις αλλο γένος [metabasis eis allo genos]” (LI, § 2, 13) changes the foundation of knowledge into Mill’s “mere assemblage of psychological chapters” (LI, § 13, 30), cited above.
As an example of this unnoticed metabasis, Husserl identifies the problematic fusion of logic and psychology. Formal logic—the systematic inquiry into the formal structures of reasoning—is by its very nature independent of experience, whereas psychology investigates human experience. As Husserl points out, the merging of these two different types of investigation constitutes the metabasis leading to “the setting up of invalid aims” because “the employment of methods [is] wrong in principle, not commensurate with the discipline’s true objects.” Disregarding, or forgetting, that formal logic is independent of experience, “the genuinely basic propositions and theories are shoved, often in extraordinary disguises, among wholly alien lines of thought, and appear as side-issues or incidental consequences” (LI, § 2, 13). This category mistake, as we would call it today, following Gilbert Ryle,34 or the conflation of dissimilar categories by treating them as the same, “can have the most damaging consequences” for understanding the lines of inquiry that are the aims of each science (LI, § 2, 13). By treating heterogeneous categories as the same (psychology, based on empirical investigations leading to hypothetical “laws of nature”; and logic, with its formal laws), empirical psychology is mistakenly posited as the foundation of formal knowledge. Since Aristotle, on the contrary, knowledge, by definition, is about principles that are timeless. In our modern phraseology, principles are independent of our mental states, which are happenings in the world. According to Husserl’s Logical Investigations, this confusion obliterates the genuine importance of logic as the system of a priori rules that guides our thinking and is important also for the empirical scientific method. If the art—τέχνη (technē)—of thinking is based on our psychological makeup, or, as Husserl puts it, is “a psychologistically determined technology of correct thinking,”35 then judgments become a set of relativistic propositions, lacking any firm basis against which we can discriminate as to which statements are true and which are not.
At the beginning of Logical Investigations, Husserl observes that doctrines put forward by representatives of psychologism—which for Husserl is skepticism and relativism at its worst—amount to nothing less than “bellum omnium contra omnes” (LI, § 1, 11).36 Reason is reduced to our experience here and now and explained on the empirical basis only. As a consequence, there is no independent foundation that can serve as the ground for evaluation of our different claims about the world. Any and every opinion is declared “true,” leading to a war of all against all, because if all claims are supposedly correct, there is no possibility whereby we might “separate individual conviction from universally binding truth.” If experience is all that is left to us, there is nothing to guide us toward the truth of our assertions. The normative character of our reasoning cannot be based on temporal experience because this experience is relative to our situation here and now. For Husserl, then, the initial motive for the critique of knowledge must be to revisit “questions of principle”—this “task [. . .] must ever be tackled anew” (LI, § 2, 12).
PHILOSOPHY OF ARITHMETIC
In Philosophy of Arithmetic, Husserl’s first book, he is concerned with the concepts, such as “unity, multiplicity and number,” that are “fundamental to human knowledge on the whole” (14). As he notes, since these concepts are not established clearly, they give rise to “the considerable difficulties that accrue to their understanding,” thereby instituting “dangerous errors and subtle controversies” (PA, 14). He cautions that we need to inquire into the foundation of knowledge by making clear to ourselves the basic presuppositions from which our claims proceed (ILI, § 12, 59). Only “through patient investigation of details” can we become aware of the foundations that our knowledge is based on (PA, 5; ILI, § 6, 33–34). For Husserl, “if we are not to be shattered on the rocks of extreme scepticism” (LI, § 6, 17), the path of “painstaking criticism” (PA, 5) must be traveled repeatedly (LI, § 3, 13).
As already noted, Philosophy of Arithmetic is based on “psychological researches,” because Husserl starts from the prevailing assumption of his age that “psychology [is] the science from which logic in general and the logic of the deductive sciences had to hope for philosophical clarification.” Yet he had begun to doubt the reigning wisdom of his time, according to which logic was reduced to psychology. As he says, “Such a psychological foundation never came to satisfy me” (LI, § 2). Gottlob Frege’s review of Husserl’s book reaffirmed his already changed understanding.37 The announced second volume of Philosophy of Arithmetic was never published.
It would be erroneous, however, to assume that Husserl’s first book is unconnected to his later work. Already in Philosophy of Arithmetic, Husserl shows that science can proceed, and proceed well, even though the foundational basis on which science rests is overlooked, or even forgotten. As he cautions, this state of affairs will eventually give rise to problems. In the first instance, this realization leads Husserl to question those beliefs that conflate logic and psychology. Thus Husserl turns to the problem of psychologism38 and anthropologism.
It is imperative to remember that Husserl (along with Frege) attacks “logical psychologism.”39 In Germany, the appeal to psychologism, as Jitendra Nath Mohanty explains, had probably first been made by Benno Erdmann. For Erdmann, psychologism is the “thesis that the logical principles such as the principle of non-contradiction derive their necessity from ‘the essence of our