From Substance to Structure
Abstract
The essay presents a historical arc from classical substance metaphysics to process-oriented and structural alternatives. Descartes and Leibniz establish the substance framework and its difficulties; Hume and James dismantle substance; Whitehead supplies a systematic process ontology; phenomenology and enactivism supply experiential and biological elaborations; it is recognized that phenomenology is better treated as a methodological constraint rather than as a competing ontology; autopoiesis is treated as a concrete case of relational organisation that is neither substance nor bare relation; Ladyman closes with ontic structural realism. The recurring motif is that of the shared world (pre-established harmony, inherited pasts, structural coupling). The issue is not merely that phenomenology and enactivism concern the mind–world relation rather than fundamental physics, but that their constitutive relations operate at a different scale and with different modal commitments from the modal structures of ontic structural realism.
Descartes
Descartes advanced a substance dualism comprising two kinds of created substance: thinking substance (res cogitans) and extended substance (res extensa), whose essences are thought and extension respectively. Each human mind is a distinct finite substance united with a particular body. He located their interaction in the pineal gland, without providing a mechanism that would reconcile the ontological disparity between the unextended and the extended. Having argued for God’s existence (Meditations III and V), he maintained that a non-deceiving God guarantees the reliability of clear and distinct perception, including the existence of bodies (Meditation VI). Two difficulties remain prominent. The first is the Cartesian Circle: the reliability of clear and distinct perception appears to be presupposed in the proof of the God who is then invoked to underwrite that reliability. The second is the interaction problem, pressed by Princess Elisabeth of Bohemia, concerning how substances of heterogeneous natures can causally affect one another.
Leibniz
Leibniz retained the concept of substance while rejecting both Cartesian dualism and inter-substantial causation. His substances are monads: simple, unextended, “windowless” units, each characterised by perception and appetition (only some attaining self-conscious apperception). Matter and space are not substances but well-founded phenomena arising from the perceptual states of monads. Because monads cannot act upon one another, the systematic correlation of their perceptions requires explanation. Leibniz appealed to a pre-established harmony instituted by God, such that each monad mirrors the entire universe from its own point of view.
Hume
Hume denied that we possess any impression, and therefore any intelligible idea, of substance (Treatise 1.4.3, 1.4.5–6). What we call a “thing” is a collection of qualities bound by the imagination and designated by a name. He treated the mind analogously, as a bundle of perceptions. For Hume the relations among perceptions, including causation, are external: we observe constant conjunction, never necessary connection.
James
In “Does ‘Consciousness’ Exist?” (1904), James denied that consciousness is an entity and treated it as a function – namely, knowing. Drawing on Avenarius (and, more loosely, Mach), he introduced “pure experience” as a single neutral “stuff” that functions as mental or physical according to context, and is therefore not a substance in the Cartesian sense. Against Hume, his radical empiricism holds that relations, both conjunctive and disjunctive, are directly experienced and as real as the terms they relate.
Whitehead
In Process and Reality (1929), Whitehead, drawing on Leibniz, Locke, Hume and James, replaced enduring substances with events. The final real things are momentary “actual occasions” (or “actual entities”). Unlike monads, they are not windowless: each arises by “prehending” (feeling) earlier occasions, which enter constitutively into its being. Concrescence is the process whereby a plurality of data is unified into a single occasion; it is not the merging of several occasions. The subject is not a pre-existing entity but emerges in the process and perishes into objective data available to subsequent occasions. Occasions share a world because they inherit overlapping pasts. God is retained as a principle that supplies relevance and initial aim, not as the author of a pre-established harmony. The system remains technically demanding.
Phenomenology
Phenomenology continues the shift initiated by James and Whitehead by beginning from experience rather than from substance. Husserl’s founding claim is that consciousness is always consciousness OF something. Act and object are constituted together; intentionality is therefore an internal relation that addresses Hume’s bundle theory from within experience itself. His analysis of time-consciousness (the 1905 lectures) describes a thick present comprising retention of the just-past and “protention” of the about-to-be – a structure that parallels, without historical dependence upon, Whitehead’s prehension of earlier occasions.
Heidegger (Being and Time, 1927) discards the subject–object framework. Dasein is being-in-the-world; there is no worldless subject whose access to the world requires a divine guarantee. The Cartesian problem is thereby dissolved rather than solved. Merleau-Ponty (Phenomenology of Perception, 1945) introduces the lived body (Leib), which is neither res cogitans nor res extensa. The subject is already bodily and worldly, so the interaction problem does not arise. Concerning the shared world, Husserl’s Fifth Cartesian Meditation derives intersubjectivity from transcendental empathy between embodied subjects, whom he even terms “monads,” though without pre-established harmony.
A caveat is required. Husserl’s epoché brackets metaphysical questions, and his later work tends toward transcendental idealism. Phenomenology is therefore better understood as a method that constrains ontology than as a finished rival ontology. Whitehead’s realism cannot simply be assimilated to it.
Enactivism
Varela, Thompson and Rosch (The Embodied Mind, 1991) join the phenomenological lived body to Maturana and Varela’s concept of autopoiesis: a living system is a self-producing organisation that generates its own boundary and its own domain of significance. Cognition is “enaction” – the co-determination of organism and world through structural coupling. Thompson’s Mind in Life (2007) argues for a deep continuity between life and mind; Di Paolo’s notion of sense-making further articulates the bridge.
This development bears directly on the problem of a shared world. Leibniz invoked God; Whitehead appealed to overlapping inherited pasts. Enactivism offers a naturalistic alternative: a shared world is enacted through ongoing coupling among organisms and between organisms and their environments. The relations are constitutive, since organism and environment mutually specify one another. No pre-established harmony is required, nor is an entirely independent external world posited as the sole unifying principle.
Autopoiesis supplies a concrete instance of an entity that is neither substance nor bare relation: a self-maintaining pattern of processes whose components are sustained by their relational organisation. Neurophenomenology (Varela, 1996) proposes a methodological response to Chalmers’ “hard problem of consciousness” by correlating first-person phenomenological reports with dynamical neural descriptions rather than reducing one to the other.
Three cautions apply. Enactivism is not monolithic: autopoietic, sensorimotor (O’Regan and Noë, 2001) and radical (Hutto and Myin, 2013) versions diverge, especially on the status of representational content. Many enactivists refrain from metaphysical commitment, so the affinity with process ontology remains suggestive rather than doctrinal. Thompson and others have drawn on Whitehead, yet this engagement is not central to the field. Finally, both phenomenology and enactivism address primarily the mind–world relation rather than the ontology of fundamental physics; their constitutive structures therefore sit uneasily with the naturalism of Ladyman and Ross.
Ladyman
Putnam’s “no-miracles” argument holds that the success of science would be miraculous were theories not approximately true. Laudan’s pessimistic meta-induction cites past empirically successful theories now regarded as false. Worrall (1989) proposed epistemic structural realism as a middle path: what is preserved across theory change is mathematical structure. Ladyman (1998) developed the ontic version (OSR), according to which structure is ontologically fundamental. In Ladyman and Ross’s Every Thing Must Go (2007), objects are derivative of, or constituted by, relational structure – not merely mathematical structure, but physical and modal structure.
The Apparent Dilemma
Either reality consists of substances possessing intrinsic natures, in which case relations are external and their coordination is difficult to explain (interaction, causation), or reality consists of relations, in which case, one appears to be left with relations without relata. The second horn is the standard objection to OSR and has been met by moderate formulations in which relata exist yet depend upon relations. The dilemma is not exhaustive. Whitehead’s internal relations furnish a third option: the related items are constituted by their relations. Phenomenology and enactivism supply that option with experiential and biological grounding – intentionality and structural coupling are relations that constitute their relata. Autopoietic systems illustrate the point most clearly, being processes sustained by their own relational organisation. The tension with Ladyman and Ross persists, however, because the constitutive relations of phenomenology and enactivism operate at the scale of organism and experience, whereas OSR concerns the modal structure of fundamental physics. Whether these two levels of structure can be coherently related remains an open question.