Change

Although his predecessors had theories to account for natural changes, Heracleitus (c. 540–c. 480 b.c.e.) seems to be the first Western thinker to raise philosophical questions about change itself. According to Plato, Heracleitus held that (1) all things are changing, and (2) comparing life to a river, he claimed that one could not step twice into the same river (Cratylus 402a). On the basis of these two theses Plato draws the conclusion that (3) Heracleitus maintained that contradictory propositions were true (Theaetetus 182–183). In fact, Heracleitus seems to have held a more defensible, if still radical, view. Plato probably derives (1) and (2) directly from Heracleitus fr. 12: "On those stepping into the same rivers, other and other waters flow." Instead of saying the rivers are different, Heracleitus says they are the same—in contrast to the waters that comprise them. From this and other fragments we can extract a theory that although there is constant change in the materials of the world, stable structures supervene on them. Indeed, Heracleitus seems to imply that if there were not constant exchanges of matter, the structures would not exist; for instance, if the water ceased to flow, the river would cease to be.

The Eleatic challenge.

In contrast to Heracleitus, Parmenides (b. c. 515 B.C.E.) of Elea (possibly reacting to Heracleitus, though this is controversial) denies the possibility of change. Rejecting the way "that it is not" because what-is-not could not be uttered (fr. 2), Parmenides rules out whatever properties rely on not-being. Since coming to be or perishing presuppose a time when something is not, they are not allowed, and similarly motion (in place?) is to be rejected (fr. 8). Parmenides enumerates several kinds of change: "coming to be and perishing, being and not being, changing place and exchanging bright color" (fr. 8.40–41). He seems to reject all of these as impossible. Parmenides' argument presents a problem often called the "Eleatic challenge": how can what-is come from what-is-not? The challenge poses a direct threat to cosmogony, the standard kind of pre-Socratic theory. After Parmenides, most cosmological theories posited the existence of a plurality of continuing materials that were individually supposed to be everlasting, for instance the four elements of Empedocles (c. 490–c. 430 B.C.E.): earth, water, air, and fire. Thus cosmologists could claim that they did not allow coming to be or perishing of the ultimate realities, but only a harmless rearrangement of them. Nonetheless, Parmenides' argument seems to rule out not only coming to be and perishing, but all other kinds of change as well, and also to preclude a plurality of existences. Reinforced and sharpened by Zeno of Elea (c. 495–c. 430 B.C.E.) and Melissus of Samos (5th c. B.C.E.), the Eleatic challenge seems to have gone unanswered for more than a century.

Plato's response.

Perhaps influenced by the lectures of Cratylus (a follower of Heracleitus), Plato (c. 428–348 or 347 B.C.E.) attributes a radical flux to the world of sensible things: they are always changing and never completely stable. If sensible things were the only existing things, knowledge and even discourse about the world would be impossible. But there is another world of changeless realities, the Forms, which provide a stable structure for sensible things, referents for language, and objects for knowledge. Forms, such as Justice and Equality, and perhaps Bed, have Parmenidean properties but no Heracleitean properties. Thus Plato creates a two-world theory, in which Heracleitean change of sensible things is tempered by Parmenidean constancy of ideal things. In his later work, Plato even posits a Form of Motion and another of Rest as ultimate kinds in which all sensible things participate (Sophist 254d). Unfortunately, a Form of Motion does not allow for any analysis of different kinds of motion or of different stages within a motion. Plato claims that the ultimate source of orderly motion is soul, which is immortal and self-moving (Phaedrus 245c–e).

Aristotle.

Aristotle (384–322 B.C.E.) provides the first systematic study of change. He maintains that only primary substances can survive a change of one property to its opposite, implying that changes are variations in properties over time (Categories 5). He distinguishes several types of change by the kind of entity involved: coming-to-be and its opposite perishing (change in the category of substance), alteration (change of quality), increase and decrease (change of quantity), and locomotion (change of place) (ibid. 14). In Physics I, he sets out to answer the Eleatic challenge. Observing that changes always involve a subject changing from one opposite state to another, he generalizes this scheme to the most problematic case: that of change in substance. Even in this case there is some continuing subject for a change from one state to its opposite, as in the case of bronze, which goes from being unformed to being formed (in a statue). Similarly, there is some continuing sub-stratum for something going from being not-human to human; the substratum for substantial change can be called matter (e.g., bronze), the negative state the privation (e.g., not-formed), the positive state the form (e.g., formed). On this model, though the final object comes from what-is-not, it does not come from nothing: the negative state is not nonexistence, but characterizes something that is, e.g., the bronze. "What-is-not" is seen to pick out not-F, and to presuppose a matter m, and not to refer to nothing at all. The Eleatic challenge rests on a mistake.

Aristotle sets out the circumstances of change as follows: a cause of motion M causes an object O to change from condition (place, property, etc.) C ₁ to C ₂ between times t ₁ and t ₂ (Physics V 1). In those cases in which O does not come to be or perish (undergo change of substance), the change is a motion. We may identify the circumstances with identity conditions: two changes are the same just in case they have the same mover, object, initial and final conditions, and beginning and ending times.

Not satisfied with a general definition and defense of change, Aristotle seeks to identify its place in the cosmos. Some things are always in motion (e.g., the heavenly bodies), some always at rest (e.g., the earth), and some things are at different times in motion and at rest (e.g., animals). Because there can be no beginning of time, but time is only the measure of regular motion, there must always have been cosmic motion. The only kind of motion that can be everlasting is locomotion in a circle (seen in the heavenly bodies). Such everlasting motion is only possible if there is some unmoved entity that causes the motion (Physics VIII). This is the first unmoved mover, which acts as a final cause, so that the heavenly bodies try to imitate its perfect (but motionless) actuality. Aristotle assumes that motion needs some sort of explanation, and everlasting motion needs an everlasting cause.

Christian Platonism.

Throughout late antiquity and the Middle Ages, Platonic and Aristotelian concepts of change continued to provide the standard account. There is, however, one important departure from classical theories that early Christian thinkers made: beginning in the second century C.E. they began to claim that God created the world ex nihilo (out of nothing), contrary to the classical notion expressed by Parmenides that what-is could not come from what-is-not. The Creation was a miraculous event caused by an omnipotent God.

Later Platonists interpreted Plato as saying that there was a simple and perfect One from which Mind (including the Platonic Forms) emanated; from Mind, Soul emanated, and from Soul, matter. Emanation was a kind of ontological overflowing according to which one being gave of its fullness to produce a lower-level being; the lower being proceeds from the higher in a timeless way such that the lower is always in existence, but dependent on the higher. Temporal distinctions are found only in the lower beings, so that the One and Mind are not in time and hence not subject to change.

In Christian Platonism, both ex nihilo creation and a changeless deity are combined with a historical account of God's interaction with the world, as in St. Augustine of Hippo's (354–430) City of God. Paradoxically, a changeless God interacts with changeable mortals to produce the drama of human salvation.