I am having a difficult time understanding the critique of psychologism. From Dan Zahavi's book Husserl's Phenomonology:

Logic (as well as, for instance, mathematics and formal ontology) is not an empirical science and is not at all concerned with factually existing objects. On the contrary, it investigates ideal structures and laws, and its investigations are characterized by their certainty and exactness. In contrast, psychology is an empirical science that investigates the factual nature of consciousness, and its results are therefore characterized by the same vagueness and mere probability that marks the results of all the other empirical sciences (Hua 18/181). To reduce logic to psychology is consequently a regular category mistake that completely ignores the ideality, apodicticity (indubitable certainty), and aprioricity (nonempirical validity) characterizing the laws of logic (Hua 18/79-80). * These features can never be founded in or explained by reference to the factual-empirical nature of the psyche.

Why can't something like Logic be reduced to Psychological laws if it is something that originates from the brain? Even if Logic is capable of having apriori truths such as 1+1=2, isn't that still a process of the brain and subject to psychological study? Is Logic not built upon certain mechanisms within the brain? I am very confused on the argument against Psychologism.

  • 2
    Husserl wrote a whole book (Logical Investigations, vol. I) with arguments for anti-psychologism in logic, see SEP summary. But an obvious one is that any such "reduction" will be circular, it will involve reasoning and hence will rely on the very logic it attempts to reduce. Second, logic is normative, it prescribes ways of reasoning, and "mechanisms in the brain" prescribe nothing, they just are. "Reducing" prescriptions to descriptions is the naturalistic fallacy.
    – Conifold
    Apr 5 '17 at 22:02
  • What is meant by it being normative and prescriptive? Also what is the nature of such terms that are used such as practical-normative? Why is the "-" used and how should it be read? Apr 7 '17 at 22:36
  • The argument in the quote is essentially this: we have a great deal more confidence in logic than in empirically discovered psychological laws, so the idea that the former derive from the latter is absurd. Logic may be implemented in our brains to some degree (not very well, as the wide spread occurrence of fallacies shows), but studying it has as little to with psychology as with brain chemistry. Just as binary arithmetic implemented on the computers has little to do with electric laws.
    – Conifold
    Mar 4 '19 at 6:59
  • I struggle to see his argument. There seems no reason why the 'laws of thought' could not originate in the mind. But it would require that everything originates in the mind and Husserl may not have considered this loophole. .
    – user20253
    Mar 5 '19 at 12:04

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