Rationality in Psychology and Philosophical Naturalism

Rationality in Psychology and Philosophical Naturalism

Thomas Sturm

Philosophical naturalists claim that we should use empirical psychological knowledge for answering epistemological questions. Critics usually object that naturalistic epistemology is limited by the existence of apriori knowledge, or by the impossibility of deriving or explaining norms from facts. Thomas Sturm used a different procedure to evaluate naturalism. By analyzing current psychological research on human reasoning, he reflected on how far and under what conditions psychology can deliver what naturalists hope it does. Psychologists (e.g., Kahneman & Tversky, Nisbett & Ross) have often followed the Is-Ought distinction when studying whether humans reason according to norms of logic or probability theory. Some researchers, however, have criticized the "blind" acceptance of such norms (e.g., Cosmides, Gigerenzer et al.). The question of how we ought to reason, they claim, cannot be answered independently of the contents and contexts of reasoning. Hence, psychology would have a lot to say about the validity of reasoning norms. By analyzing psychological debates about reasoning, one can show that psychologists evaluate and improve our reasoning in different ways. For instance, we need to hold apart:

  1. How we can facilitate the learning of norms
  2. Whether violations of some norms can be interpreted as rational in the light of other norms
  3. What norms subjects ought to apply to certain tasks
  4. Whether norms can only be justified in domain-specific ways

Only the fourth point undermines the view that norms are valid independently of contents and contexts of reasoning (see Sturm, 2008). On the other hand, some norms of reasoning can indeed be derived empirically (see Gigerenzer & Sturm, 2009). Psychological studies show that some heuristics require less information and computation than norms of probability or decision theory, but nevertheless deliver accurate results. Yet, there are still reasons to claim that certain norms of reasoning hold apriori. If these points are correct, a “replacement” naturalism (which aims to replace epistemology by psychology) fails. However, a “cooperative” naturalism (which claims that psychology and philosophy contribute different goods to theories of rationality) survives. In this project, Thomas Sturm clarified the potentials and limits of this naturalism further by studying, among other things:

  1. How far norms of rationality can be naturalized
  2. How far rationality can be explained by evolutionary theory, and
  3. What apriori assumptions and rules are necessary to investigate point 1 and 2


  • Sturm, T. (2008a). What is the foundation of norms of rationality? In: Philosophy: Foundations and applications. Ed. by Ansgar Beckermann, Holm Tetens & Sven Walter. Paderborn: Mentis, 189-201.
  • Gigerenzer, G. & Sturm, T. (2009). How can rationality be naturalized? Synthese.