Plato: the Theory of Forms

Plato argues that the physical world we see is a world of appearances and constant change. Behind it lies a higher, unchanging realm of perfect Forms — the true, eternal realities that particular things merely imitate.

• Every beautiful thing is beautiful because it participates in the Form of Beauty; every just act reflects the Form of Justice.
• The Forms are known by reason, not the senses — Plato is a rationalist whose method is a priori.
• The highest Form is the Form of the Good, which gives the other Forms their reality and makes them knowable, as the sun makes objects visible.

Source: the Forms, the Good and the sun analogy come from Plato's Republic. The Form of the Good is compared to the sun as the source of both being and knowledge.

The Analogy of the Cave

In the Republic Plato pictures prisoners chained in a cave, watching shadows on a wall and believing the shadows are reality. One prisoner is freed, struggles up into the sunlight, and finally sees the real world and the sun itself.

• The shadows = the everyday world of appearances we mistake for reality.
• The journey out = the painful ascent of the mind through education toward knowledge.
• The sun = the Form of the Good, the ultimate source of truth.
• The freed prisoner who returns = the philosopher, often mocked by those still trapped.

Criticism to weigh: Plato gives no proof the Forms exist; the analogy can look elitist, and it devalues the empirical world that science studies so successfully.

Reading the Cave

Aristotle: the Four Causes

Aristotle rejects a separate realm of Forms. For him, reality is this world, studied through the senses — he is an empiricist whose method is a posteriori. To explain why anything exists as it does, he identifies four causes:

• Material cause — what a thing is made of (the bronze of a statue).
• Formal cause — its shape, structure or defining form (the statue's design).
• Efficient cause — what brings it about (the sculptor and their tools).
• Final cause — its purpose or telos (to honour a person). Aristotle thinks the final cause is the most important.

Source: the four causes appear in Aristotle's Physics and Metaphysics. Aristotle sees purpose (telos) built into nature itself.

Name that cause

Plato or Aristotle?

Tap an idea, then the philosopher it belongs to.

Aristotle: the Prime Mover

Aristotle observes that things in the world are constantly changing (moving from potential to actual). This chain of change must depend on something that itself does not change — the Prime Mover, or unmoved mover.

• The Prime Mover is eternal, immaterial and perfect — pure actuality with no unrealised potential.
• It does not push things like a physical force. It causes motion as a final cause, by being the object of attraction and desire — everything is drawn toward it.
• Its only activity is thought thinking itself, contemplating the highest object: itself.

Source: the Prime Mover is developed in Metaphysics Book 12 (Lambda). Note it is not a personal, loving creator like the God of the Bible — it does not know or love the world.

How does the Prime Mover move things?

Plato vs Aristotle: which is stronger?

The two thinkers model two whole approaches to philosophy of religion:

• Plato is a rationalist: real knowledge comes from reason grasping eternal Forms beyond the senses. Critics say this is unverifiable and pessimistic about the physical world.
• Aristotle is an empiricist: knowledge begins in observation, and purpose is found within nature. Critics say a final cause need not be a god, and modern science explains apparent purpose without one.

Both shape later theism: Plato's Good and Aristotle's Prime Mover feed into Aquinas' arguments for God. Whether either succeeds depends on whether a priori reason or a posteriori observation gives more secure knowledge.

Two methods

The four causes

Tap a cause on the left, then its meaning on the right.

The highest Form

The big ideas to take into the exam

You can now compare a priori and a posteriori routes to ultimate reality — the foundation of the arguments for God. Press Finish for your score.