Parallelism and Complementarity: The Psycho-Physical Problem in Spinoza and in the Succession of Niels Bohr

  • Hans Jonas
Part of the Boston Studies in the Philosophy of Science book series (BSPS, volume 91)


The psycho-physical problem named in the title of this paper was born together with modern science in the seventeenth century and is the twin brother of its guiding axiom that things corporeal must be explained by corporeal causes alone, or that the latter are sufficient to explain everything in the physical realm, neither requiring nor even admitting the cooperation of mental causes. Indeed, completeness of intraphysical determination excludes the introjection of any non-physical source of action. So put, the axiom — in a stunning break with pre-modern, ‘Aristotelian’ physics — amounts to the thesis of a causal redundancy of mind in nature. This redundancy found its first expression in the disavowal of ‘final causes,’ the concept of which is somehow borrowed from mentality. At the root of the radical turn was a reinterpretation of ‘nature’ itself in purely spatial or geometrical terms. This made measurement of magnitudes the main mode of scientific observation, and quantitative equation of cause and effect, i.e., of antecedents and consequents, the ultimate mode of explanation. This epistemic program of the new science received its metaphysical underpinning in Descartes’ doctrine of two heterogeneous kinds of reality (‘substances’ in his language) — the res externa and the res cogitans — each defined by its one essential attribute ‘extension’ and ‘thought’ respectively, and each having nothing in common with the other.


Twin Brother Physical Necessity Intrinsic Reference Quantum Mechanical Case Causal Redundancy 
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  2. Jonas, Hans: 1974, Philosophical Essays. From Ancient Creed to Technological Man, Chicago University Press, Chicago.Google Scholar
  3. Spinoza, Benedicti de: 1930, Ethica ordine geometrico demonstrata, transl, by William Hale White, in John Wild (ed.), Spinoza, Selections, Charles Scribner’s Sons, New York.Google Scholar

Copyright information

© D. Reidel Publishing Company 1986

Authors and Affiliations

  • Hans Jonas
    • 1
  1. 1.New School for Social ResearchUSA

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