Heymans’s Psychic Monism

Philosopher and psychologist Gerard Heymans’s psychic monism is an empirically motivated idealism holding that all real processes are psychical and that physical phenomena, brain processes included, are the way psychical processes appear to perceiving minds. Advanced in his Einführung in die Metaphysik auf Grundlage der Erfahrung(Introduction to Metaphysics on the Basis of Experience) (1905) as an explanatory hypothesis on a par with atomic theory, it takes phenomenal consciousness to be the one reality known directly and as it is, and physical science to be relational knowledge of its structure. Heymans argued that what is perceived as a brain process is, in itself, the subject’s conscious process, then extended the psychical series inward to unconscious processes and outward to all of nature, arriving at a Fechnerian hierarchy of consciousnesses within a world consciousness—leaving unexplained, by his own admission, how individual consciousnesses are demarcated within the psychical whole (Heymans, 1905; Bruining, 1905; Dekker, 2011).

In other words, Heymans’s psychic monism interprets phenomenal consciousness as the directly encountered reality whose outward appearance is physical activity. Rather than deriving experience from intrinsically nonexperiential matter, Heymans proposed that brain processes are consciousness as indirectly perceived, and extended this interpretation to nature generally. Individual minds are concentrations of psychical processes within a wider experiential order, potentially encompassing Earth, larger cosmic systems, and a World Consciousness. Developed as an empirical metaphysical hypothesis under Gustav Fechner’s influence, the theory seeks to reconcile subjective experience, mental causation, and physical law. Its principal unresolved issue concerns the unity and individuation of consciousness (Heymans, 1905, 1915; Dekker, 2011).

Metaphysics as Explanatory Hypothesis

Heymans held that metaphysical systems are explanatory hypotheses in the same sense as the atomic and molecular theory or the mechanical theory of heat: conceptual constructions not abstracted from the given but devised to make it intelligible, and therefore answerable to the same standards (Heymans, 1905; Bruining, 1905). The Einführung accordingly proceeds as a graded comparison of world-hypotheses—naive realism and dualism, materialism, parallelism, the doctrine of an unknown “Other,” positivism, and absolute skepticism—each tested against the data until its difficulties force the next step, in Heymans’s view, ending in psychic monism (Heymans, 1905).

Against Materialism, Dualism, and the Unknown Other

Against materialism, in both its “equative” form (consciousness is brain process) and its “causative” form (brain process produces consciousness), Heymans argued that matter cannot account for subjective experience, the one datum given directly; developments in physics concerning energy, electromagnetism, and atomic structure had, moreover, made matter far less self-contained than classical materialism assumed (Heymans, 1905; Dekker, 2011). Interactionist dualism multiplies substances needlessly once a coherent single-substance account is available (Dekker, 2011). Parallelism and Spinozist dual-aspect theory fare better but face two objections. If mental events never act causally, conduct would proceed exactly as it does without volition—a consequence Heymans rejected. More decisively, a dual-aspect view admits a physical series that, on its own premises, could never be perceived, since every perception is itself psychical; an unknowable third reality behind both series therefore explains nothing the psychical series cannot (Bruining, 1905). Positivism, finally, cannot account for the order within experience: the causal principle requires that this order have causes outside individual consciousness, and these causes must themselves be psychical (Heymans, 1905).

Phenomenal Consciousness and the Brain as Appearance

Heymans distinguished absolute knowledge of a thing as it is in itself from relative knowledge of its relations to other things, and held that natural science yields only the latter (Heymans, 1905; Bruining, 1905). Conscious states are known absolutely: given immediately, non-inferentially, and as they are. Physical objects are hypothetical constructions describing lawful relations among possible perceptions. Elevating parallelism from heuristic to ontology, Heymans proposed that the realities which, under favorable conditions, would produce perceptions of brain processes are the conscious processes themselves (Heymans, 1905). An observer looking into another’s skull would perceive tissue; for its owner, that same reality is experience and nothing but experience (Hermans, 2009). The brain process is thus not a correlate of phenomenal consciousness but its appearance in another mind. On this view, the explanatory gap is epistemic rather than ontological: experience is what the process is, and the neural description is how it registers from outside. Because the physical series is the psychical series as perceived, consciousness is not epiphenomenal; physiological causation is psychical causation described relationally (Heymans, 1915; Dekker, 2011). Bruining (1905) objected that this makes psychic monism a mirror image of materialism, an objection that turns on whether the mechanical description has reality beyond appearance.

Completing the Psychical Series

Conscious life taken alone is causally incomplete, so Heymans supplemented the psychical series “inward” with processes outside consciousness that obey the same causal laws as conscious ones. He then supplemented it “outward”: as the brain process is the appearance of a consciousness, every physical process is the appearance of some psychical process, so that the psychical is coextensive with nature (Heymans, 1905; Bruining, 1905). His laboratory work fit this picture. Studies of psychical inhibition showed that the threshold for one stimulus rises in proportion to the intensity of a competing stimulus—Heymans’s law—implying that the ordinary sensory threshold is itself an inhibition phenomenon (Heymans, 1899). Entry into awareness is thus graded and competitive, set by the relative strength of contents rather than by a fixed boundary between mental and non-mental.

World Consciousness and the Problem of Individuation

Following Fechner, Heymans considers increasingly comprehensive consciousnesses associated with cells, organisms, Earth, the solar system, and larger cosmic systems. The progression culminates in a World Consciousness. Individual human experience becomes one scale of organization within a potentially much wider hierarchy (Heymans, 1905, 1915).

The central analogy concerns integration: experiences already form organized unities, so more extensive interaction might support more encompassing consciousnesses. However, greater interaction among people or cosmic components does not by itself demonstrate a further subject for whom those interactions are experienced together. The hierarchy remains a speculative extrapolation, not a finding of psychophysics.

The broader framework also motivated Heymans’s telepathy experiments of the early 1920s: if minds are regions of one psychical system, connections bypassing the senses are not excluded in principle (Dekker, 2011). Apparently separate minds might retain connections within this more comprehensive consciousness; another person’s thought becoming accessible could be compared with one’s own previously inaccessible thought returning to awareness. While this interpretation helped energize his psychical research, the proposed explanatory framework must be distinguished from verification of the phenomena themselves (Kloosterman, 2014).

Individuation and Explanatory Limits

Yet here the framework meets its limit. Why the psychical whole is partitioned into bounded individual consciousnesses whose contents are mutually inaccessible, and how integration yields a unified subject, Heymans did not explain; he conceded that “the fact of individuation thus remains a problem” (Heymans, 1905, as quoted in Bruining, 1905).

The central difficulty is why psychical processes belong together as one experience, and why that experience is distinct from another subject’s. Heymans acknowledged that increasing interaction does not explain why initially distinct processes must constitute a unified consciousness. In responding to criticism, he also rejected the attribution to him of independently existing “psychical atoms” accidentally merging into minds (Heymans, 1906, pp. 311–313).

His position thus leaves open the constitution of experiential subjects while taking their unity as an empirical starting point. He expressly presents psychic monism as an open inquiry, allowing that further questions about the ground of psychical reality may exceed the available evidence (Heymans, 1906). In contemporary terms, it encounters both the combination problem of panpsychism—how experiential elements constitute a subject—and the individuation problem of idealism—how finite subjects relate to a more encompassing consciousness. These are retrospective comparisons, not Heymans’ own contemporary taxonomy.

Psychic monism relocates the explanatory burden from the emergence of experience out of nonexperience to the organization, differentiation, and physical manifestation of experience. Its historical significance lies in making consciousness central to an empirically informed metaphysics. Its limitation is the absence of a sufficiently specified account of subjective unity or independently discriminating evidence for its universal extension.

Legacy and Assessment

Heymans’s position belongs to the fin-de-siècle revival of panpsychist and idealist monism associated with Fechner and Paulsen, but differs from absolute idealism in resting on experimental psychology and hypothetico-deductive method rather than dialectic (Hermans, 2009). Its structure anticipates several positions in the Landscape: the contrast between relational physical knowledge and intrinsic experiential nature prefigures Russellian Monism; the nested hierarchy culminating in a world consciousness, with its attendant individuation problem, parallels debates over Cosmopsychism; and the thesis that brain states are the outward appearance of experience recurs in Kastrup’s Analytic Idealism, which addresses individuation through dissociation. These are structural resemblances, not documented lines of influence. Heymans’s claim to empirical standing rests on the explanatory reach of the whole system rather than on any decisive observation.

Acknowledgment

Kars Dekker, whose doctoral research (PhD, History of Psychology) examines Heymans’s consciousness theory and methodology, proposed this entry and supplied the expert draft on which it is in part based.

References

Bruining, A. (1905). Wetenschappelijke metaphysica: Dr. G. Heymans, Einführung in die Metaphysik auf Grundlage der Erfahrung [Scientific metaphysics], I–II. De Gids, 69, 310–333; 482–506.

Dekker, K. (2011). Gerard Heymans herlezen: Bewustzijn en methodologie [Rereading Gerard Heymans: Consciousness and methodology] (Doctoral dissertation, University of Groningen). Groningen: WB Uitgeverij.

Hermans, C. (2009). Omwenteling onder het schedeldak: Gerard Heymans en de hervorming van de psyche [Revolution under the skull: Gerard Heymans and the reform of the psyche]. In I. de Haan, W. ten Have, J. Kennedy, & P. J. Knegtmans (Eds.), Het eenzame gelijk: Hervormers tussen droom en daad, 1850–1950. Amsterdam: Boom.

Heymans, G. (1899). Untersuchungen über psychische Hemmung: Erster Artikel [Investigations of psychical inhibition: First article]. Zeitschrift für Psychologie und Physiologie der Sinnesorgane, 21, 321–359.

Heymans, G. (1905). Einführung in die Metaphysik auf Grundlage der Erfahrung [Introduction to metaphysics on the basis of experience]. Leipzig: Johann Ambrosius Barth.

Heymans, G. (1915). Het psychisch monisme [Psychic monism]. Zenuw- en zieleleven, Series 4, No. 2. Baarn: Hollandia-Drukkerij.

[Convention note: Heymans (1905) is cited by first-edition date. The second, revised and enlarged edition (Leipzig: Barth, 1911) substantially expanded the chapter on psychic monism (§§30–38, including §36 “Die Ergänzung der psychischen Reihe nach innen,” §37 “… nach außen,” and §38 “Das Problem der Individuation”); a third edition appeared in 1921, and a Dutch translation (Amsterdam: Wereldbibliotheek, 1933) carries a foreword by Leo Polak.]