3.3.2 - Ontological arguments

The A Priori Ambition

Most arguments for God's existence begin with something in the world: order, causation, contingency, religious experience or morality. Ontological arguments try something stranger. They ask whether God's existence follows from the concept of God itself.

It is a priori because its key premises are meant to be knowable through reason or conceptual analysis, independently of sensory evidence. It is normally deductive because it aims to show that, if the premises are true, the conclusion must follow.

That ambition creates the central philosophical pressure:

Can a concept be so special that understanding it commits you to the existence of its object?

For ordinary concepts, the answer seems no. You can understand the concept of a perfect painting, a flawless island or a unicorn without thereby proving that any such thing exists. Ontological arguments claim that God is not an ordinary case. God is supposed to be the greatest conceivable being, a supremely perfect being, or an unlimited necessary being. If the concept is genuinely that unique, perhaps existence is not an optional extra.

Key terms:

AQA asks you to pay attention to three things:

The three arguments in this lesson share an a priori and deductive ambition, but they do not make exactly the same move. Anselm begins with the greatest conceivable being. Descartes begins with a supremely perfect being whose essence includes existence. Malcolm reframes the issue in terms of necessary existence and impossibility.

Anselm: Understanding And Reality

AQA names Anselm's set text as the Proslogium, Chapters II-IV. Many editions call the same work the Proslogion. Anselm's first main move is found in Chapter II.

Anselm defines God as the greatest conceivable being: that than which nothing greater can be conceived. The argument begins by granting that even the person who denies God can understand this phrase. If they understand it, the concept is in the understanding. Anselm then compares two ways something can be present:

Anselm's key thought is that existence in reality is greater than existence in the understanding alone. If God existed only as an idea, we could conceive of something greater: the same being existing in reality. But that would contradict the definition of God as the greatest conceivable being.

The argument can be reconstructed like this:

Claim at issue: God exists in reality, not only as an idea.

1. P1: God is the greatest conceivable being.
2. P2: Even someone who denies God can understand the concept of the greatest conceivable being.
3. P3: What is understood exists at least in the understanding.
4. P4: A being that exists in reality as well as in the understanding is greater than a being that exists only in the understanding.
5. P5: If God existed only in the understanding, a greater being could be conceived: God existing in reality.
6. P6: But no being greater than God can be conceived.
7. Therefore, C: God exists in reality.

Hidden assumption: existence in reality is a greatness-making feature.
Inference type: a priori deductive reductio; Anselm assumes the denial and derives a contradiction.
Main pressure point: whether P4 really allows movement from a concept to real existence.

The strength of the conclusion is high. Anselm is not arguing that God probably exists or that belief in God is a good explanation. He is trying to prove that God does exist, because denying God's real existence conflicts with the concept of God as greatest conceivable being.

The nature of God assumed here is not first described through omnipotence, omniscience or omnibenevolence. Those attributes matter elsewhere in AQA metaphysics of God. Here the starting point is more abstract: God is unsurpassably great. Anselm's later chapters connect that unsurpassable greatness with divine attributes, but the Chapter II proof itself turns on the relation between understanding, reality and greatness.

Why it is initially plausible: if God is genuinely defined as unsurpassable, then treating God as merely imaginary seems unstable. An imaginary greatest being would apparently be surpassed by a real greatest being. Anselm's argument feels powerful because it turns the atheist's understanding of the word God into the starting point of the proof.

Anselm: Necessary Existence

Chapter III strengthens the argument. Anselm does not only want to say that God happens to exist. He wants to say that God cannot be conceived not to exist. This is the move from existence to necessary existence.

You, this lesson, a tree, a mountain and a planet are all normally treated as contingent. A necessary being, by contrast, cannot fail to exist. It does not depend on lucky conditions, causes, composition or timing.

Anselm's Chapter III reasoning can be reconstructed like this:

Claim at issue: God exists necessarily.

1. P1: God is the greatest conceivable being.
2. P2: A being that cannot be conceived not to exist is greater than a being that can be conceived not to exist.
3. P3: If God could be conceived not to exist, then a greater being could be conceived: one just like God but impossible not to exist.
4. P4: No being greater than God can be conceived.
5. Therefore, C1: God cannot be conceived not to exist.
6. Therefore, C2: God exists necessarily.

Hidden assumption: necessary existence is a greatness-making feature.
Inference type: a priori deductive reductio.
Main pressure point: whether necessary existence is genuinely built into the concept of the greatest conceivable being.

The strength of the conclusion is stronger than God does exist. It is God must exist, or God's non-existence is not properly conceivable once the concept is understood. This matters for AQA because ontological arguments often defend a God whose existence is unlike the existence of ordinary things.

Chapter IV then explains how someone can still say the words God does not exist. Anselm's answer is that there are two levels of conceiving:

So Anselm is not denying that an atheist can pronounce a sentence. He is claiming that, if the concept is properly understood, the denial fails at the level of thought. The lesson boundary is important here: Gaunilo's perfect island objection tests whether this style of reasoning can be parodied. That objection is taught in the next lesson. Here the point is only that Anselm thinks God is a unique case because God is not merely a very good member of a kind; God is the being whose non-existence would be incompatible with unsurpassable greatness.

Why it is initially plausible: necessary existence seems greater than fragile or dependent existence. A being that can fail, depend, decay or be prevented looks less ultimate than one whose existence is secured by its own nature. This makes Anselm's Chapter III move attractive to defenders who think the real target is not bare existence but necessary existence.

Descartes: Essence And Perfection

AQA sets Descartes' Meditations on First Philosophy, Meditations 3 and 5. The ontological argument itself is most directly in Meditation 5, but Meditation 3 matters because it supplies Descartes' idea of God.

In Meditation 3, Descartes describes God as an infinite, eternal, unchangeable, independent, supremely intelligent and supremely powerful substance. He also treats the idea of God as the idea of a supremely perfect being. The causal argument in Meditation 3 is not the ontological argument, and Descartes' argument from continuing existence belongs with cosmological arguments later in 3.3.2. Here, Meditation 3 is useful because it tells us what concept of God Descartes brings into Meditation 5.