Introduction to Arguments Based on Reason

Welcome to one of the most fascinating parts of Philosophy of Religion! So far, you may have looked at arguments for God’s existence based on observation (like looking at a watch or the stars). This chapter is different. Here, we look at arguments based on reason, specifically the Ontological Argument.

Instead of looking outside at the world, these arguments look inside at the very definition of the word "God." The goal is to show that if you truly understand what "God" means, you must admit that God exists. Don't worry if this seems a bit "mind-bending" at first—it is meant to be! We will break it down step-by-step.

Key Concept: A Priori vs. A Posteriori

Before we dive into the argument, we need to understand two vital terms used in your exam:

1. A Posteriori: These are arguments based on observation and experience. (Example: "I know it is raining because I can see the water.") The Teleological and Cosmological arguments are a posteriori.

2. A Priori: These are arguments based on reason and logic alone, independent of experience. (Example: "A triangle has three sides." You don't need to go find a triangle to know this; it’s true by definition.) The Ontological Argument is a priori.

Quick Tip: Think of A Priori as "Prior" to looking at the world. You use your brain first!

Anselm’s Ontological Argument

Anselm was an 11th-century Archbishop who wanted to show that even a "fool" (someone who denies God) must logically admit God exists. His argument is found in his book, the Proslogion.

Anselm’s Definition of God

Anselm starts with a specific definition: God is "that than which nothing greater can be conceived."

In simpler terms: God is the greatest thing you can possibly imagine. If you think of something and then think of something even better, then the first thing wasn't God!

Proslogion 2: Existence in Reality

Anselm argues there are two ways to exist:
1. In the mind (in intellectu).
2. In reality (in re).

Anselm uses the analogy of a painter. A painter has an idea for a great painting in their mind. However, once they paint it, the painting exists in both the mind and reality. Surely, a painting that actually exists is "greater" than one that is just a thought?

The Logic: If God is the "greatest thing imaginable," and it is "greater" to exist in reality than just in the mind, then God must exist in reality. If He didn't, we could imagine something greater (a God who does exist), which contradicts our definition!

Proslogion 3: Necessary Existence

Anselm takes it further. He argues that God’s existence is necessary.
- Contingent things: Things that can start or stop existing (like humans, trees, or cars).
- Necessary things: Things that must exist and cannot not exist.

Anselm argues that a being that must exist is greater than a being that just happens to exist. Therefore, because God is the greatest being, He must have necessary existence.

Key Takeaway: Anselm believes God's existence is a logical necessity. To say "God does not exist" is like saying "A square has three sides"—it is a contradiction in terms.

Gaunilo’s Challenge: "In Behalf of the Fool"

A monk named Gaunilo was a contemporary of Anselm. He didn't necessarily doubt God, but he thought Anselm’s logic was flawed. He wrote a response titled "In Behalf of the Fool."

The Perfect Island Analogy

Gaunilo used a reductio ad absurdum (showing an argument is "absurd" by following its logic to a ridiculous conclusion). He asked us to imagine the "Perfect Island":
1. I can imagine the most perfect island (lost somewhere in the ocean).
2. It is "greater" to exist in reality than just in my mind.
3. Therefore, according to Anselm’s logic, this perfect island must exist.

The Point: We know the perfect island doesn't actually have to exist just because we can define it. Gaunilo argued you cannot "define" things into existence.

Anselm's Response: Anselm argued that his logic only applies to God. An island is contingent (it relies on things like water and land to exist) and can always be improved (more coconuts, better sand). God is the only necessary being, so the argument only works for Him.

Kant’s Criticism: Existence is not a Predicate

Centuries later, Kant provided what many consider the most famous "takedown" of the Ontological Argument.

What is a Predicate?

A predicate is a word that describes something or adds information to it. For example, if I say "The cat is black and fluffy," "black" and "fluffy" are predicates. They tell you something about the cat's nature.

Kant’s Argument

Kant argued that "existence" is NOT a predicate. Saying something "exists" doesn't actually add any descriptive information to the concept of the object.

The 100 Thalers Example:
Imagine 100 gold coins (Thalers). I can describe them: they are round, shiny, gold, and heavy. These are predicates. If I then say "...and they exist," I haven't added any new characteristics to the coins. The 100 existing coins aren't "more" or "better" than the 100 imagined coins in terms of their description.

The Conclusion: Because existence doesn't make God "greater" (since it's not a descriptive quality), Anselm’s logic falls apart. You can define God however you like, but you still have to go outside and check if that definition matches reality.

Discussion: Is the Argument Persuasive?

In your exam, you may be asked to discuss whether a priori or a posteriori arguments are more successful.

Strengths of Arguments based on Reason (A Priori):
- They provide certainty if you accept the premises. Like \(2 + 2 = 4\), the conclusion is inescapable if the logic holds.
- They don't rely on messy, changing scientific evidence or unreliable senses.

Weaknesses:
- Many people feel like Gaunilo and Kant: you can't just "define" God into existence.
- For someone who doesn't already believe in God, the definition "the greatest thing imaginable" might not mean anything at all.

Did you know? Many philosophers believe Anselm wasn't actually trying to "convert" atheists. Instead, he was writing a prayer to show how his faith was supported by his reason!

Quick Review Box

  • Anselm: Defined God as "that than which nothing greater can be conceived" and argued that existing in reality is greater than just existing in the mind.
  • Gaunilo: Challenged Anselm with the "Perfect Island"—you can't define things into existence.
  • Kant: Argued that existence is not a predicate; it doesn't add anything to a definition.
  • A Priori: Knowledge based on logic/reason (like the Ontological Argument).
  • A Posteriori: Knowledge based on observation (like the Teleological Argument).

Common Mistake to Avoid: Don't confuse the Ontological Argument with the Design (Teleological) Argument. Remember: The Ontological Argument uses no evidence from the world—it is purely a "brain-teaser" of logic!

For more on arguments based on observation, see the chapter: "Arguments based on observation."