Being, Motion, Time

Continuing the Question of Time

The companion guide On Time traced a question — what is time? — from Plato's cosmological heavens, through Husserl's flowing present, to Heidegger's mortal, ecstatic Dasein. Between Plato and Husserl, however, sits a seventeenth-century interlude that guide passed over: the three great systems of Continental Rationalism. Each of these thinkers inherits the ancient link between being, motion, and time — what exists, how it changes, how it endures — and each reworks that link in a strikingly different direction, often in direct argument with one another.

Descartes splits reality into thinking substance and extended substance, then must explain how his own method of doubt ever gets off the ground without circularity. Spinoza, appalled by the resulting dualism, collapses everything into a single infinite substance. Leibniz, dissatisfied with both, shatters substance into an infinite plurality of simple, windowless monads. Each move has direct consequences for how each thinker treats motion (is it fundamental, or merely phenomenal?) and time (is it a real container, an eternal backdrop, or a merely ideal order?) — consequences this guide traces section by section, closing with an explicit look back at how each anticipates or contrasts with Plato, Husserl, and Heidegger.

The Cartesian Circle

Descartes' Meditations on First Philosophy (1641) opens by doubting everything that can possibly be doubted — the senses, the external world, even mathematics, under the hypothesis of a deceiving demon. The one thing that survives is the act of doubting itself: cogito, ergo sum — "I think, therefore I am." From the certainty of the cogito, Descartes extracts a general principle, his provisional rule of truth: whatever is perceived clearly and distinctly is true.

But the demon hypothesis threatens even this rule — what if some clear and distinct perceptions are themselves implanted errors? Descartes' answer is to prove, using clear and distinct perception, that God exists and, being perfect, cannot be a deceiver. Once God's veracity is established, clear and distinct perception in general is guaranteed reliable, memory of past proofs included.

The French theologian Antoine Arnauld, in the Fourth Set of Objections appended to the Meditations, spotted the problem immediately: Descartes uses clear and distinct perception to prove God exists, and then uses God's existence to guarantee that clear and distinct perception is reliable. The very faculty on trial is called as the star witness for its own defense.

Descartes' own reply, developed in the Second Replies and in Meditation Five, distinguishes perceptions currently held before the mind — which compel assent by their sheer clarity, needing no external guarantee in that instant — from conclusions merely remembered to have once been proven, which could in principle be undermined by a deceiver tampering with memory. God's veracity, on this reading, secures only the second case. Whether this fully escapes the circle remains debated: constructing the proof of God's existence is itself a multi-step argument that requires holding earlier premises in mind while reasoning to later ones — which looks uncomfortably close to relying on the very memory-trust the argument is meant to secure. The Cartesian Circle remains, appropriately for its subject, unresolved in a fully clean and distinct way.

Being — Two SubstancesRes Cogitans, Res Extensa

Descartes defines substance, strictly, as that which needs nothing but itself to exist — a definition only God fully satisfies. Loosely, he still applies the term to two created kinds of finite substance, distinguished by their principal attribute: res cogitans, thinking substance, whose essence is thought, and res extensa, extended substance, whose essence is extension in three dimensions. In Meditation Six, Descartes argues that because he can clearly and distinctly conceive mind without body and body without mind, God could create either without the other — establishing, for Descartes, that they are really distinct substances, not two aspects of one thing.

This dualism immediately generates the notorious interaction problem: if mind and body are utterly different kinds of substance, one unextended and thinking, the other extended and unthinking, how can a decision in the mind move an arm made of matter? Descartes' own strained answer — interaction via the pineal gland — persuaded almost none of his successors, and both Spinoza and Leibniz built their systems partly in reaction against it.

Motion — The Plenum

Because Descartes identifies body with extension, and extension is simply geometric space, he denies the possibility of a vacuum: wherever there is space, there is body, so the universe is a single continuous plenum. Motion is defined relationally, as the transfer of a body from the vicinity of the bodies immediately touching it into the vicinity of others — and since there is no empty space for a body to move into, motion in a plenum always takes the form of a closed loop or chain of bodies displacing one another simultaneously, which is why Descartes' cosmology fills the heavens with swirling vortices of subtle matter carrying the planets around the sun.

Descartes grounds his three laws of motion — inertia, rectilinear tendency, and rules for collision — in the immutability of God, who conserves a constant total quantity of motion (size multiplied by speed, summed across the universe) from moment to moment, precisely because God's own unchanging nature guarantees that the total activity he originally imparted to the world is never increased or diminished.

Time — Continuous Creation

Descartes' most startling doctrine about time is metaphysical rather than physical. In Meditation Three, reflecting on his own continued existence, he notes that "the whole time of my life can be divided into innumerable parts, each one of which in no way depends on the others" — so that his existing now provides no guarantee whatsoever that he will still exist a moment later. Conserving a thing in existence, he concludes, requires exactly the same creative power God used to make it in the first place: existence is sustained only by a continuous, moment-by-moment re-creation.

Separately, and more conventionally, Descartes follows the Aristotelian tradition in distinguishing duration — a general mode by which a thing continues to exist — from time strictly speaking, which is duration measured and numbered by comparison with the regular motion of some body, such as the sun's yearly circuit. The radical doctrine of continuous creation operates beneath this more familiar surface picture of time-as-measured-motion.

Being — Deus Sive NaturaOne Substance, Infinite Attributes

Spinoza's Ethics (1677), composed more geometrico in the style of Euclid — definitions, axioms, propositions, proofs — begins from a definition of substance nearly identical to Descartes': "that which is in itself and is conceived through itself." Where Descartes allowed two created substances alongside God, Spinoza presses the definition to its limit: nothing dependent on anything else can be a genuine substance, so there can be only one — infinite, uncaused, existing by the sheer necessity of its own nature. Spinoza calls this substance, indifferently, God or Nature — Deus sive Natura.

This single substance possesses infinitely many attributes expressing its essence, of which finite minds can grasp only two: Thought and Extension — precisely Descartes' two "substances," demoted by Spinoza to mere attributes of the one substance. Every particular mind and body is not a substance in its own right but a finite mode, a way that infinite substance happens to express itself, exactly as a wave is a temporary modification of the sea rather than a thing existing independently of it. Because thought and extension are attributes of one and the same substance, mind and body are, for Spinoza, "one and the same thing, expressed in two ways" — dissolving Descartes' interaction problem by denying there were ever two separate substances to interact in the first place.

Motion — Motion-and-Rest

In a physical digression following Proposition 13 of Ethics Part II, Spinoza explains how the single attribute of Extension gives rise to the varied physical world. Directly following from Extension is what Spinoza calls its immediate infinite mode: motion-and-rest, the most basic, universal principle of physical change, from which follows a mediate infinite mode, the "face of the whole universe" (facies totius universi) — the total, ever-shifting yet eternally self-identical pattern of the entire physical cosmos, considered as a single infinite individual.

Individual finite bodies, in turn, are defined not by any fixed stuff but by a stable ratio of motion-and-rest maintained among their constantly-exchanged parts — an early, strikingly structural or functional account of what makes a body the same persisting individual over time, prefiguring later ideas about organisms and systems defined by pattern rather than material.

Time — Eternity and Duration

Spinoza draws a sharp line between two ways of being temporal. Eternity (aeternitas) belongs to substance alone: existence following necessarily from the mere definition of an eternal thing, involving no before or after whatsoever — not endless duration, but the exclusion of temporal succession altogether. Duration (duratio), by contrast, is the "indefinite continuance of existing" proper to finite modes, each one causally dependent on other finite things in an endless chain, existing at particular times.

The structural resemblance to Plato's Timaeus is striking: Spinoza's eternity, like Plato's aiôn, "abides in one" without succession, while duration, like Plato's chronos, is the successive mode in which finite things exist — though Spinoza relocates the whole relation inside a single immanent substance, with no external Demiurge required to stamp time onto matter.

Being — MonadsWindowless, Perceiving, Harmonized

Leibniz rejects both Descartes' two substances and Spinoza's one. In the Monadology (1714), he argues reality ultimately consists of infinitely many simple, non-extended, indivisible immaterial substances: monads. Each monad is a unique perceiving point of view that internally "mirrors" or represents the entire universe, with a clarity ranging from the barely-perceiving "bare monads" that make up ordinary matter, through animal souls capable of sensation and memory, up to rational spirits capable of self-conscious reflection.

Monads are famously windowless — nothing passes into or out of them causally. Every monad's internal states unfold entirely from its own nature, following a built-in "law of the series" that constitutes its complete individual concept. The universe-wide appearance of coordinated causal interaction — a struck billiard ball, a decision moving an arm — is arranged in advance by God through pre-established harmony: like an enormous collection of perfectly synchronized clocks, each running independently, yet always in perfect mutual agreement, with no clock ever actually causing another to tick.

What we ordinarily call matter or extended body, on this view, is not fundamental at all: it is a phaenomenon bene fundatum, a "well-founded phenomenon" — a coherent appearance arising from the confused, low-clarity aggregate perceptions of countless monads, genuinely grounded in monadic reality without itself being that reality.

Motion — Vis Viva Against Descartes

Leibniz mounted a direct, technical challenge to Cartesian physics. Descartes had claimed that quantity of motion — mass times speed (mv) — is conserved throughout the universe. Leibniz, using a thought experiment involving falling bodies, showed this cannot be right: what is actually conserved in elastic collisions is vis viva, "living force," proportional to mass times the square of speed (mv²). This "vis viva controversy" occupied physicists for decades and anticipated the later distinction between momentum (always conserved) and kinetic energy (conserved only in elastic collisions) — both Descartes and Leibniz, in retrospect, had identified genuinely conserved quantities, just not the same one.

Leibniz's physics also carried a metaphysical consequence: since he held that space is nothing but the ideal order of coexisting things — not, as Newton claimed, an absolute container existing independently of the bodies in it — motion itself, strictly speaking, is also phenomenal, grounded in shifting relations among monadic perceptions rather than movement through an absolute void. Leibniz defended this relational view at length against Newton's absolute space and time in his correspondence with Samuel Clarke (1715–16).

Time — An Ideal Order of Successions

Just as space is the order of coexisting things, Leibniz holds that time is the ideal order of successive things — not an absolute, self-standing container that would exist even in an empty universe, but a relational structure grounded in the sequence of changes among things. Against Clarke's Newtonian defense of absolute time, Leibniz argued that if the entire universe had been created five years earlier than it actually was, with every relation between things exactly preserved, nothing detectable — indeed nothing meaningful — would have changed, which he took to show that time adds nothing over and above the order of successive states of the world.

Three Metaphysics of Being

Toggle between the three pictures of substance to see how each rationalist redraws the most basic map of what exists.

Comparative Table

Echoes of Plato, Husserl, and Heidegger

Read against the earlier guide, each rationalist's treatment of time lands in a recognisably different spot on the same map.

Taken together, the two guides sketch a long arc: from time stamped onto the heavens by a craftsman god, through time sustained instant-by-instant by a conserving God, through time as the eternal backdrop of a single immanent substance, through time as a harmony pre-arranged across infinitely many perceiving points, to time as first constituted within the flow of a single experiencing consciousness, and finally to time as the finite, mortal horizon of an existence that must die. Every step keeps returning to the same three words: being, motion, time.

Lineage

Glossary