Change

Plato inherits two rival legacies. Parmenides taught that what is must be one, changeless, and eternal; becoming is illusion. Heraclitus taught the opposite: everything flows, nothing remains. Plato's response is to distinguish two orders of reality and assign each position to its proper domain. The sensible realm, which is always changing and never fully is, yields only opinion; the intelligible realm of the Forms, which always is and never changes, is the object of genuine knowledge.

The Theaetetus examines what follows if everything changes in every respect at every moment: nothing can be named, for by the time the word is uttered, the thing has already become other. Knowledge requires a stable object, and change taken to its limit destroys that stability. The Timaeus provides the cosmological account: the visible world is a "moving image of eternity," fashioned by the Demiurge after the pattern of the unchanging Forms, impressed upon a receptacle of space. The Sophist then refines the analysis, admitting motion itself among the "greatest kinds" and refusing to identify being simply with rest or immobility.

On Plato's account, the knowability of things depends on their having a stable character that does not shift from moment to moment. Change in the sensible world is always change of something, toward something, in imitation of a Form that itself does not change. Whether this division between the realm of being and the realm of becoming adequately explains natural things, or whether the Forms are too remote from sensible particulars to serve as principles of their explanation, is among the principal questions Aristotle raises against the Platonic theory. The distinction between the mutable and the immutable, and its bearing on the possibility of knowledge, is further discussed in the chapters on Being and Eternity.

Plato transmits to subsequent thinkers the demand that change be understood in terms of something that does not itself change. Aristotle will accept this demand while refusing the Platonic solution, finding the required permanence not in Forms separate from things but in the unchanging essences that belong to changing substances themselves. The question of how to account for the reality of becoming without sacrificing the possibility of knowledge remains one of the central problems in the philosophy of nature.

Aristotle answers Parmenides directly. The Eleatic denial of change rested on a false dichotomy: either a thing is or is not. Aristotle interposes a third term: potentiality. What changes neither springs from sheer non-being nor remains simply what it already was; it was potentially F and becomes actually F. Matter and form, together with privation, give change its three unchanging principles. The substrate persists; one contrary gives way to another; the composite is transformed.

With this framework the Physics distinguishes four kinds of change: in substance (generation and corruption), in quality (alteration), in quantity (growth and decay), and in place (locomotion). Each is the actualization of a potency in the respect in which it is still potential. The leaf turning red is partly actually green and potentially red; while the change is under way, its potentiality to be red is being actualized, but not yet completed. Motion is thus an incomplete actuality, a being-on-the-way. Local motion is primary, since the others presuppose it, and the eternal circular motion of the heavens requires, at the summit, an unmoved mover: pure actuality with no potency left to actualize.

If change has principles, nature is intelligible and a science of natural things is possible, against both the Eleatics who denied change and the flux-philosophers who made it too radical for knowledge. Whether all types of change are equally real or reducible to one another divides Aristotle sharply from Descartes and the later mechanists, who identify motion exclusively with change of place. The question of whether the analysis of change requires the concepts of potency and act, or can be carried out in purely mathematical and mechanical terms, constitutes one of the central disputes in the philosophy of nature, and is discussed further in the chapters on Cause and Matter.

Aristotle's account of change dominates natural philosophy for two millennia. The decisive shift comes in the seventeenth century, when Descartes declares that the actualization of potency is unintelligible and replaces it with a mechanical account: a body is located somewhere, and change is the fact that it is now located somewhere else. The Aristotelian vocabulary of potency and act survives thereafter primarily in metaphysics and theology, as the chapter on Cause indicates.

Lucretius, expounding Epicurus, rejects the Aristotelian apparatus wholesale. There is no potency, no form, no unmoved mover. There are only atoms and the void. Every change we observe, whether birth, growth, alteration, or decay, is at bottom a rearrangement: atoms coming together, separating, swerving, colliding. Nothing comes from nothing, and nothing returns to nothing; the total stock of matter is fixed, and change is nothing but the reshuffling of its indestructible parts.

The atoms themselves neither come to be nor pass away, nor do they alter in quality or size. Their only motion is local motion through empty space. From this single kind of change all apparent variety is generated: colors, tastes, living bodies, minds, whole worlds arise and dissolve as combinations of particles meet and part. The void is indispensable, for without empty space there would be no room for motion at all. Even the soul is a fine texture of atoms, dispersed at death.

Lucretius presents the Epicurean account of nature explicitly as a remedy for the anxieties that religion has imposed on human life. If the gods do not govern natural processes and the soul does not survive the body's dissolution, the fear of divine punishment and of suffering after death loses its ground. Change is material and mechanical throughout; no Forms, no final causes, and no immaterial souls are required to explain it. The connection between the physics of change and the ethics of equanimity is, for Lucretius, as direct as it is essential: understanding the mechanism of change is the first step toward peace of mind. The swerve of atoms, departing from strict necessity, preserves room for what Lucretius regards as voluntary action, relating the physics of change to questions discussed under the ideas of Fate and Necessity.

Lucretius transmits ancient atomism to the Latin world, and through it to the seventeenth century. When Descartes, Gassendi, and Hobbes reduce all change to local motion, they are reviving an idea Lucretius had already pressed with incomparable poetic force.

Plotinus carries to a further extreme the Platonic distinction between being and becoming. Change, on his account, marks distance from the source of all reality. The One is beyond being, beyond motion, beyond multiplicity. From it proceeds Intellect (Nous), and from Intellect the Soul, and only at the level of Soul does time and change arise. The sensible cosmos is the shadow of Soul in matter, always becoming because it can never fully contain the intelligible pattern it imitates.

In Enneads II.5, Plotinus takes up Aristotle's distinction between potency and act and turns it against him. At the highest levels, there is no potency at all: Intellect is pure actuality, and the One is above even that. Potency belongs to matter, which is sheer indeterminacy, a kind of non-being that receives form without ever becoming anything in its own right. Change in the sensible world is the flickering of forms over this receptive darkness: real, but derivative, and always tending back toward the source from which it fell.

If change marks distance from the One, then the philosophical life consists in retracing the procession: turning inward and upward from the flux of bodies through the soul to Intellect and, in rare moments, to union with the One itself. Becoming is not to be explained away but to be transcended; motion is the condition of incompleteness, and rest in the One is the soul's true condition. This metaphysics of procession and return exercises a deep influence on the tradition of theology discussed in the chapters on Being and Eternity, where the questions of immutable and mutable existence are pursued more fully.

Plotinus fuses Platonic transcendence with Aristotelian act, and hands Christian theology a metaphysics in which God is absolutely unchanging and creation is a procession of diminishing degrees of being. Augustine will take the structure but insist on a difference that reshapes it entirely: for Plotinus, the soul's return is a philosophical necessity written into its nature; for Augustine, it depends on grace freely given by a God who can be refused.

The most searching ancient meditation on time and change arrives not in a physics treatise but in a personal prayer. Augustine, in the eleventh book of the Confessions, asks what God was doing before he made heaven and earth, and immediately dissolves the question. There was no "before." Time itself is a creature; to ask what preceded creation is to presuppose a temporal container independent of creation, which is the very thing that cannot be granted. Change and temporal succession begin together, as twin features of a world made from nothing.

This move has precise philosophical substance. Augustine draws on Plotinus's account of time as the image of eternity, but carries the argument in a different direction. For Plotinus, time and eternity are structural features of the procession of the One; the soul generates time by its unfolding activity. For Augustine, both time and the soul are created from nothing by a free divine act. The eternal present of God is not the apex of a hierarchy that includes time below it; it is the altogether different mode of a Creator who stands outside the order he has made. "In the Eternal, nothing passeth, but the whole is present." Time, on this account, is the soul's distension — a stretching of experience into memory, present attention, and expectation. Change is not primarily a metaphysical structure of matter and form; it is the mark of creaturely existence.

Augustine's analysis connects the metaphysical question of change to the spiritual restlessness that gives the Confessions its opening theme. The soul in time is always moving toward or away from something; it cannot rest in what changes, because changing things do not persist in being. "Our heart is restless, until it rests in Thee." If God is pure actuality without potency, and if the soul's unrest is the mark of its own incompleteness, then natural change is the outward expression of the soul's condition: real, but derivative, and always pointing beyond itself. This connection between change in the world and the soul's orientation toward the eternal is developed further in the chapters on Eternity and the Soul.

The vision of an eternal, changeless God against the backdrop of a world in constant temporal flux becomes the central inheritance that medieval theology receives from Augustine. Aquinas will systematize the distinction between divine immutability and creaturely becoming; but the question Augustine presses — how the soul finds rest in what does not change — shapes the tradition's attitude toward change from within, not merely as a technical problem but as a question about the ultimate meaning of becoming.

Aquinas takes Aristotle's analysis of change and sets it within a Christian metaphysics of creation. Every motion in the natural world is the actualization of a potency by something already in act, and every such series of movers and moved must terminate in a first mover that is pure act: actus purus. This is the famous first way to God. Natural change thus confirms, rather than replaces, the classical framework: matter, form, and privation remain the principles of becoming.

But Aquinas introduces a distinction that Aristotle could not make. Creation ex nihilo is not a change. Change requires a subject that was potentially F and becomes actually F; creation presupposes no prior subject at all. "In creation," Aquinas writes, "by which the whole substance of a thing is produced, the same thing can be taken as different now and before only according to our way of understanding." God's causing of the world is therefore unlike any natural process: it is the giving of being simply, not the transformation of something already there. God himself is absolutely immutable, for pure act contains no potency that could be actualized.

Several consequences follow from the distinction between change and creation, bearing on the theological questions treated in the chapters on God and Eternity. If creation is not a change, the question of whether the world has always existed cannot be settled by appeal to the nature of change alone; Aquinas holds, against those who thought reason could prove the world's eternity, that this question is determined only by revelation. If God is immutable, the divine decrees do not shift with the world's becoming, and Providence can be understood without attributing change to God. And if natural change genuinely requires a first mover in pure act, then physics itself raises a question that natural reason may take up, even if it cannot settle it without assistance from elsewhere.

Aquinas gives the Aristotelian theory of change its canonical Christian formulation. When Descartes and the moderns reject potency and act, they are dismantling a structure that had organized natural philosophy, theology, and metaphysics together.

Bacon's attack on scholastic natural philosophy centers on a complaint about how change is explained. The Aristotelian tradition accounts for change by appeal to forms, qualities, and final causes — vocabulary that Bacon finds verbal rather than real. To say that heat is a quality that makes things hot, or that fire moves upward because its natural place is above, is to clothe ignorance in learned words. The Novum Organum argues that the entire inherited method is backwards: it rushes from a few observations to general principles and then deduces downward, when the only productive path runs upward, from careful history of natural instances through graduated generalization to genuine law.

What Bacon calls the inquiry into "latent process" is the attempt to describe the actual stages through which change proceeds rather than the nominal form it instantiates. When iron rusts, or wax melts, or seed germinates, something passes through a series of intermediate states invisible to casual observation; the task of natural philosophy is to reconstruct those stages empirically. Bacon retains the word "form" but redefines it radically: a Form is not a metaphysical constituent of a substance but the invariable causal law governing a particular nature, the complete set of conditions upon which it depends. To know the Form of heat is not to contemplate a universal but to be able to produce or suppress heat at will. The practical and the theoretical are, for Bacon, continuous: power over natural change and knowledge of its laws are the same thing.

Bacon's version of inquiry into change is less mathematical than the program Galileo and Newton execute, and his specific proposals for inductive method have often been found inadequate to the science he hoped to inspire. His contribution is less methodological recipe than imaginative reorientation: the conviction that the investigation of nature must begin with experience rather than with a priori principles, and that the goal of natural philosophy is command over natural processes, not contemplation of fixed essences. Whether Bacon's empirical orientation and Newton's mathematical laws represent the same program or different ones is a question discussed further under the ideas of Induction and Science.

Bacon does not carry the analysis of change into mathematics; it falls to Newton to formalize the causal laws of motion that Bacon's program demands. But the shift Bacon initiates — from explaining change by appeal to essence and finality to explaining it by reference to invariant causal laws discoverable through observation — is the shift that the scientific revolution as a whole puts into practice, whatever its precise method.

Galileo's most consequential contribution to the understanding of change is less a discovery than a reconceptualization of what requires explanation. Aristotle had maintained that every motion requires a cause continuously in contact with the moved, because rest is the natural terminus of every body and sustained motion is a departure from that terminus. Galileo's experiments with inclined planes and his analysis of projectile motion lead him to deny the premise. A ball rolled on a perfectly smooth horizontal surface would continue to roll indefinitely without any further cause. What requires explanation is not motion but change of motion — acceleration and deceleration.

This apparently technical point reorganizes the entire analysis of natural change. If rest is no more natural than uniform motion, the Aristotelian distinction between natural and violent motion loses its force, and with it the whole apparatus of natural places and tendencies toward rest. Galileo replaces the qualitative vocabulary of natural places with a mathematical description of quantities: the distance fallen is proportional to the square of the time elapsed, the path of a projectile is a parabola, the period of a pendulum depends on its length alone. Change in nature is not the passage from privation to form but a measurable relationship between continuously varying quantities. Mathematics, Galileo argues in the Dialogue, is the language in which the book of nature is written, and those who read it in any other idiom read it wrong.

Galileo also transforms the method of inquiry. Where Bacon advocates induction from natural history, Galileo combines mathematical hypothesis with idealized experiment: he imagines frictionless planes and perfectly spherical balls in order to isolate the quantities that matter, then checks the resulting laws against what can actually be measured. The interplay of mathematical deduction and controlled observation, not the accumulation of cases, is what produces secure knowledge of how things change. This methodological combination, more than any particular result, is what Newton inherits. Whether the idealization required by mathematical physics is a legitimate procedure or a concealed departure from the natural world is a question raised again under the idea of Mechanics.

Galileo reformulates the central question of motion from "why does this body move?" to "why does this body accelerate?" The reformulation is far more tractable and far more productive. Newton will generalize it into universal laws; Descartes will build a physics of pure extension on a neighboring foundation; but both work within the framework Galileo establishes by insisting that natural change is a mathematical quantity, not a qualitative passage between states.

Descartes rejects the Aristotelian conception of motion as philosophically unacceptable. The Scholastic definition, the actualization of what exists in potentiality insofar as it is potential, is, in his view, obscure rather than explanatory. "Who understands these words?" he asks in the Principles. Motion, properly speaking, is nothing more than "the transference of one part of matter or of one body from the vicinity of those bodies that are in immediate contact with it... into the vicinity of others." There is no mysterious becoming; there is only a body, actually somewhere, and then actually somewhere else.

The consequences ramify through all of physics. If motion is simply local motion, every other kind of change (qualitative alteration, growth, even substantial generation) must be reduced to the rearrangement of extended matter in motion. Matter is res extensa, and change is the reshuffling of its parts. God set the total quantity of motion in the universe at creation and conserves it; all particular motions are transfers of this quantity among bodies. A moving body is completely actual at every instant of its motion; it needs no cause to sustain it, only to alter or stop it.

On the Cartesian account, change in nature becomes intelligible precisely because it is reduced to local motion, which can be expressed in the language of geometry and measured by the calculus. What Descartes regards as the obscurity of the older vocabulary (form, final cause, potency) is replaced by the clarity of extension and figure. This intelligibility is achieved, however, at the cost of formal and final causes, which had organized Aristotelian natural philosophy. Whether such causes are genuinely explanatory or merely verbal is a question discussed further under the idea of Cause.

Descartes supplies the conceptual framework on which Newton will build. After him, "change" in natural philosophy means displacement, and the Aristotelian vocabulary of potency and act survives only in metaphysics and theology.

Newton converts the Cartesian conception of motion into exact mathematical law. The first axiom of the Principia states: "Every body continues in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it." Inertia, so understood, removes the Aristotelian demand that every motion require a continuously acting mover. A body in motion keeps moving on its own; only a change of motion (acceleration) calls for a cause.

Force is what produces change of motion, and its measure is the second law: the change of motion is proportional to the motive force impressed. Local motion becomes the universal currency of natural change, and the calculus provides the tools to measure its variations. In the Preface, Newton expresses the hope that all natural phenomena might be derived "from mechanical principles, for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of bodies... are either mutually impelled towards one another, and cohere in regular figures, or are repelled and recede from one another." Chemistry, heat, light, life: all are to be reduced to particles in motion under forces.

Against the Aristotelian picture of qualitatively distinct kinds of change, the Principia treats all natural change as change of state of motion, measurable, predictable, and subject to universal law. Celestial and terrestrial motions fall under the same equations; the cosmos becomes a single mechanical system. Whether this mathematical description of change is adequate to all natural phenomena, or whether living and mental processes require principles beyond mechanics, is a question that Newton does not address in his physical work. The relation between Newton's achievement and the broader questions of metaphysics and the philosophy of nature is discussed further under the ideas of Cause and Mechanics.

Newton completes the seventeenth century's transformation of the concept of change. After the Principia, natural philosophy studies motion as a mathematical quantity. Hume will ask the question that Newton does not: not how forces are measured, but what force actually is, and whether the necessary connection we attribute to causes corresponds to anything in the objects themselves or arises only from the habit of the mind that observes them.

Hume applies empiricist analysis to the concept of change and, more particularly, to the connection by which one change is said to produce another. Newton has shown how motions succeed one another with mathematical regularity, but what exactly do we perceive when one body's change produces another's? Impact, recoil, acceleration: we observe the sequence, and we observe that it has been repeated. What we never observe is the hidden tie, the productive power, by which the first state brings the second into being.

Hume examines any case of change (a billiard ball struck by another, water boiling over a flame, a seed becoming a plant) and finds the same result: contiguity in space, succession in time, and constant conjunction across repeated cases. The idea of necessary connection is not derived from any single impression of the objects themselves; it arises only after repetition, as a felt transition in the mind from the idea of one event to the idea of its customary successor. We project this inner habit outward and attribute causes and powers to things.

Whether this analysis fatally undermines the foundations of natural science, or whether it is compatible with the practical success of science while leaving its ultimate metaphysical basis unresolved, is a question the tradition does not settle in a single voice. It may be argued that Hume's point is not that we cannot predict or explain change, but that we cannot identify, in the objects themselves, anything that corresponds to what we mean by causal necessity. The problem of induction and the problem of necessary connection are, in Hume's treatment, aspects of a single difficulty, discussed further under the ideas of Cause and Necessity.

Hume leaves the concept of change without the traditional metaphysical grounding that Aristotelian and Cartesian frameworks had provided. Change is what we observe; causal necessity is what the mind supplies. Kant will treat this conclusion as the occasion that compelled him to examine the conditions under which any coherent experience of change is possible at all.

Kant answers Hume by relocating the problem. If we never perceive necessary connection in the objects, perhaps that connection belongs to the conditions under which any object can appear to us at all. In the Analogies of Experience, Kant argues that the concepts of substance, causality, and interaction are not gleaned from experience but are a priori principles without which no coherent experience of change would be possible.

The First Analogy states that in all change of appearances, substance persists; its quantum in nature is neither increased nor diminished. The Second Analogy states that all change occurs in accordance with the law of cause and effect: every alteration has a cause that determines it to take place. These are not discoveries about the world in itself; they are rules of synthesis that the understanding imposes on the manifold of sense. Without a persistent substance, there would be no subject of change; without causal rule, there would be no objective order of succession, only a subjective flow of impressions. Change, for Kant, is thus the orderly succession of states of a substance, under law.

Kant's answer to Hume carries a cost that subsequent thinkers regard as significant. The categories of substance and causality apply only to phenomena, that is, to things as they appear in experience. Of the thing-in-itself, of whether substance really persists or causes really act apart from the conditions of experience, nothing can be known. Change, like time, is a feature of the form of experience, not of reality as it is independent of that form. This restriction of the categories to the phenomenal world, and the resulting inaccessibility of things-in-themselves, becomes one of the central points of contention in the subsequent idealist tradition. The relation between Kant's treatment of change and his analysis of time is pursued more fully under the idea of Time.

Kant secures the framework of Newtonian change against Humean skepticism, but at the cost of confining it to the phenomenal world. Hegel will refuse this confinement and take change back into the heart of reality itself.

Hegel opens the Science of Logic with an analysis that places change at the center of all philosophical inquiry. Pure Being, taken in its utter indeterminacy, is indistinguishable from Nothing: each is empty, each passes into the other. Their unity and their difference together constitute Becoming. Change is not a problem to be explained by unchanging principles; it is the first concrete concept, the truth of being and nothing alike. Parmenides and Heraclitus are both right, and dialectically reconciled.

From this opening, the Logic unfolds as a self-moving succession of categories, each passing over into its opposite and then into a higher synthesis. Reality itself has this dialectical structure, not merely our thought about it: determinate being arises, limits itself, contradicts itself, and surpasses itself. Nature and history are the external and temporal unfolding of Spirit's self-development. The Aristotelian framework of potency and act returns, transformed: every finite thing carries within it the seed of its own negation, and change is the working out of this internal tension. Against Kant, the categories are the very articulations of the real, not forms imposed on an unknowable in-itself.

If change is the truth of being, then philosophy cannot rest in any fixed opposition between substance and accident, subject and object, finite and infinite. Every determination is provisional, every stage superseded. Nature exhibits the dialectical structure in space; history exhibits it in time. On this view, the sequence from Parmenides through Aristotle to Descartes and Kant is itself a movement driven by internal contradiction, each position generating the difficulties that require the next. Whether the necessity Hegel finds in this movement is genuinely inherent in the history of thought, or is imposed upon it by the systematizer, is a question that subsequent critics have pressed with considerable force, as the chapters on History and Dialectic indicate.

Hegel closes the arc that began with Parmenides. Where the Eleatic had denied becoming to save being, Hegel dissolves being into becoming and recovers both. The question he cannot silence is whether the dialectical necessity he finds in history is genuinely there or only imputed: whether Spirit's self-development through contradiction is the structure of the real, or the structure of one philosopher's very persuasive narrative about it.