Plato & Aristotle: Forms, the Good, and the Prime Mover

Plato & Aristotle: Forms, the Good, and the Prime Mover

The philosophies of Plato (c. 428–348 BCE) and Aristotle (384–322 BCE) represent the two most influential starting points for Western philosophy and Christian theology. Though Aristotle was Plato’s student at the Academy in Athens for twenty years, the two thinkers diverged fundamentally on the question of where ultimate reality is located — a disagreement that has shaped religious thought ever since. For AQA A-Level Religious Studies (specification 7062), a thorough understanding of both thinkers is essential, as their ideas underpin arguments for God’s existence, ethical theories, and debates about the nature of reality.

Plato’s Theory of the Forms

Plato argued that the physical world we perceive through our senses is not the true reality. Instead, it is a shadow or imperfect copy of a higher, non-physical realm of perfect, eternal, and unchanging entities called the Forms (Greek: eidos or idea). The Forms are not mere concepts in the mind; for Plato, they are objectively real — more real than the physical objects we encounter in everyday experience.

• The Forms are eternal and unchanging: They exist outside of space and time. While physical objects come into being, change, and decay, the Forms remain perfect and immutable.
• The Forms are non-physical: They cannot be perceived through the five senses but can be apprehended through reason (nous) alone.
• Physical objects participate in the Forms: A beautiful painting is beautiful because it participates in or partakes of the Form of Beauty. The painting may fade or be destroyed, but the Form of Beauty itself is indestructible.
• The Forms explain universals: The reason we can recognise different horses as “horses” is that they all participate in the Form of Horse — the perfect, universal essence of what it means to be a horse.

Plato outlined his Theory of the Forms across several dialogues, most notably the Republic, the Phaedo, and the Symposium. The theory was not static; Plato himself raised criticisms of it in the Parmenides, particularly the famous Third Man Argument, which asks: if a man resembles the Form of Man, what explains the resemblance between the man and the Form? A third entity seems to be required, leading to an infinite regress.

The Allegory of the Cave

In Book VII of the Republic, Plato presents the Allegory of the Cave — one of the most famous passages in all of philosophy — to illustrate the relationship between the world of appearances and the world of the Forms.

Imagine prisoners chained in a dark cave since birth, facing a blank wall. Behind them burns a fire, and between the fire and the prisoners, puppeteers carry objects that cast shadows on the wall. The prisoners, having never seen anything else, take the shadows to be reality itself.

The allegory unfolds in stages:

• The prisoners in the cave represent ordinary people who accept the world of sensory experience as the whole of reality. They mistake shadows (appearances) for truth.
• The escape of a prisoner represents the philosopher’s journey from ignorance to knowledge. When a prisoner is freed and turns to see the fire, they are initially blinded and confused — the process of enlightenment is painful and disorienting.
• The ascent out of the cave represents the soul’s ascent from the visible world to the intelligible world of the Forms. Outside the cave, the freed prisoner sees real objects illuminated by the sun.
• The Sun represents the Form of the Good — the highest Form, which illuminates all other Forms and makes knowledge possible, just as the physical sun makes sight possible.
• The return to the cave represents the philosopher’s duty to return and educate others, even though they will be met with ridicule and hostility. Plato intended this as an allegory for Socrates’ fate: he was executed for trying to enlighten the Athenians.

The Form of the Good

At the apex of Plato’s hierarchy of Forms stands the Form of the Good. In the Republic (Book VI, 508–509), Plato describes the Form of the Good using the Analogy of the Sun:

• Just as the sun provides light (which makes physical objects visible) and life (which sustains living things), the Form of the Good provides intelligibility (which makes the other Forms knowable) and existence (which gives the other Forms their being).
• The Form of the Good is therefore beyond being (epekeina tes ousias) — it transcends even the other Forms in dignity and power.
• Knowledge of the Good is the highest goal of the philosopher: without it, knowledge of other things is incomplete and ultimately worthless.

“In the world of knowledge the idea of the Good appears last of all, and is seen only with an effort; and, when seen, is also inferred to be the universal author of all things beautiful and right.” — Plato, Republic, 517c

The Form of the Good has been enormously influential in Christian theology. Early Church Fathers, particularly Augustine, identified the Form of the Good with God, arguing that God is the source of all goodness, truth, and being. This Platonic identification shaped centuries of Christian metaphysics and remains a live topic in the philosophy of religion.

Plato’s Dualism and the Soul

Plato was a substance dualist: he held that the soul (psyche) and the body (soma) are fundamentally different kinds of entity. In the Phaedo, Plato presents several arguments for the immortality of the soul:

• The Argument from Recollection: We can recognise imperfect instances of equality, beauty, and justice in the physical world. This suggests that the soul had prior acquaintance with the perfect Forms before birth — learning is therefore recollection (anamnesis) of what the soul already knows.
• The Argument from Affinity: The soul resembles the Forms — it is invisible, non-physical, rational, and capable of grasping eternal truths. The body resembles the physical world — it is visible, changeable, and subject to decay. Like is drawn to like: the soul is naturally drawn to the realm of the Forms.
• The Argument from Opposites: Just as sleep gives way to waking and waking to sleep, death gives way to life and life to death. The soul therefore pre-exists birth and survives death.

Plato’s dualism directly influenced Christian ideas about the immortality of the soul, the distinction between the spiritual and the material, and the notion that the body is a temporary vessel for the soul. However, it sits in tension with the orthodox Christian doctrine of the resurrection of the body.

Aristotle’s Critique and Empiricism

Aristotle (384–322 BCE) studied under Plato for twenty years but ultimately rejected the Theory of the Forms. While Plato located reality in a transcendent realm beyond the physical world, Aristotle argued that reality is found within the physical world itself. His famous dictum — attributed by later tradition — captures the difference: “Plato is dear to me, but dearer still is truth.”

Aristotle’s key objections to the Forms include:

• The Third Man Argument: If particular men resemble the Form of Man, we need a “third man” to explain the resemblance between the particular and the Form, leading to an infinite regress.
• Explanatory redundancy: The Forms do not actually explain how or why physical objects have the properties they do. Saying a beautiful painting is beautiful because it “participates in” the Form of Beauty is merely restating the problem using metaphorical language.
• Separation problem: Plato’s Forms exist in a separate realm from the objects they are supposed to explain. But how can a non-physical, non-spatial entity causally influence or relate to physical objects? Aristotle argued that forms must be immanent in (within) physical things, not separate from them.

Aristotle’s Four Causes

Aristotle proposed that to fully understand anything, we must identify its four causes (aitia), set out in his Physics and Metaphysics:

• Material Cause: The matter or substance from which something is made. (A statue’s material cause is the bronze or marble from which it is sculpted.)
• Formal Cause: The form, pattern, or essence that makes something what it is. (The statue’s formal cause is the design or blueprint — the shape of a human figure.)
• Efficient Cause: The agent or process that brings something into being. (The sculptor is the efficient cause of the statue.)
• Final Cause (telos): The purpose or end for which something exists or is done. (The statue’s final cause might be to honour a hero or to beautify a temple.)

The Final Cause is the most important for Aristotle: it is the telos — the goal, purpose, or function toward which something naturally tends. Aristotle’s philosophy is therefore teleological: he believed that everything in nature has an inherent purpose. An acorn’s telos is to become an oak tree; a knife’s telos is to cut; a human being’s telos is to live a life of rational virtue (eudaimonia).

The Prime Mover (Unmoved Mover)

In Book XII (Lambda) of the Metaphysics, Aristotle argued for the existence of a Prime Mover (or Unmoved Mover) — an eternal, unchanging, and perfect being that is the ultimate cause of all motion and change in the universe.

Aristotle’s reasoning proceeds as follows:

• Everything in the physical world is in a state of change (or motion, understood broadly to include any kind of change: growth, decay, alteration, movement in space).
• Every change is caused by something that is itself in a state of change. A hand moves a stick, which moves a stone.
• But this chain of movers cannot go back infinitely — there must be a first cause of all motion that is itself unmoved. If every mover needed a prior mover, no motion would ever have begun.
• This First Mover must be eternal (since motion is eternal), immaterial (since matter is subject to change), perfect, and unchanging.

Crucially, the Prime Mover does not cause motion by pushing things (efficient causation) but by attracting them (final causation). The Prime Mover is the ultimate object of desire and aspiration: all things in the universe are drawn toward it, as toward the supreme good. Aristotle describes the Prime Mover as engaged in eternal self-contemplation — “thinking on thinking” (noesis noeseos) — the most perfect possible activity.

“It is upon such a principle that the heavens and nature depend.” — Aristotle, Metaphysics, 1072b

Influence on Christianity

The ideas of Plato and Aristotle have profoundly shaped Christian theology:

• Plato’s influence: Early Christianity was deeply influenced by Platonism, especially through the work of Augustine of Hippo (354–430 CE). Augustine identified the Forms with ideas in the mind of God, the Form of the Good with God himself, and Plato’s dualism with the Christian distinction between body and soul, the earthly and the heavenly. Neoplatonism, developed by Plotinus (204–270 CE), provided a further philosophical framework that influenced Christian mysticism and theology.
• Aristotle’s influence: In the 13th century, Thomas Aquinas (1225–1274) synthesised Aristotelian philosophy with Christian theology, creating a system that remains central to Roman Catholic thought. Aquinas adopted Aristotle’s Four Causes, his concept of the Prime Mover (identified with God), and his teleological approach to ethics (natural law). The Prime Mover became the foundation for Aquinas’s First Way — the argument from motion — in the Summa Theologica.

Key Differences Between Plato and Aristotle

• Location of reality: For Plato, true reality is transcendent (the realm of the Forms). For Aristotle, true reality is immanent (within the physical world).
• Method of knowledge: Plato emphasised reason (nous) as the path to truth. Aristotle emphasised empirical observation and experience as the starting point for knowledge.
• Relationship of form and matter: For Plato, Forms exist independently of physical objects. For Aristotle, form is always instantiated in matter — you cannot have a form without a material instance (except in the case of the Prime Mover).
• Ethics: Plato’s ethics are oriented toward contemplation of the Form of the Good. Aristotle’s ethics are oriented toward the practical achievement of eudaimonia (flourishing) through the exercise of virtue in community.

Exam Tip: AQA examiners reward students who can clearly contrast Plato and Aristotle’s approaches and explain their relevance to later religious thought. Avoid treating them as isolated thinkers — always connect their ideas to specific theological developments, particularly Augustine (for Plato) and Aquinas (for Aristotle). Use direct references to their key works: the Republic, Phaedo, Metaphysics, and Physics.