Arguments based on reason - Anselm’s ontological reasoning
Learn the different arguments in Proslogion 2 and 3, why Anselm reasons a priori, and how to distinguish understanding a concept from establishing the existence of its object.
A concept and an a priori method
An ontological argument reasons from the concept of God towards God's existence. Anselm's Proslogion is written as prayerful enquiry by a believer seeking understanding. That context does not remove the need to test its reasoning: the argument addresses whether even someone denying God can understand a concept whose implications defeat that denial.
Anselm characterises God as a being than which no greater can be conceived. This lesson paraphrases the description rather than presenting a quotation from an unspecified translation. Greatness concerns the maximal status appropriate to God, not physical size or popular approval. The expression is intended to rule out any conceivable superior being.
The argument is a priori: its proposed justification uses the concept and rational inference, rather than observations of complexity or causation. Hearing words is how a person encounters the argument; that does not make its justification an a posteriori inference. A mathematical proof is likewise not justified by the physical ink in which it is written.
Anselm refers to the fool in the biblical setting of Psalm 14:1. His philosophical target is someone who understands the description yet denies its object exists. A crucial distinction is between in intellectu, existing in the understanding, and in re, existing in reality. The distinction lets us understand a description without assuming that there is an actual instance. The painter's imagined work and completed work illustrate that difference.
The argument must therefore do more than say we can think of God. The disputed task is whether this particular concept uniquely requires real existence.
The reasoning in Proslogion 2
Anselm's chapter 2 uses a reductio ad absurdum: temporarily assume the denial and show that it conflicts with the proposed concept. This is a method of proof by contradiction, not simply calling an opposing opinion absurd.
The reasoning can be reconstructed as follows. Even the denier understands the description of a being than which no greater is conceivable, so it exists in the understanding. Suppose it exists only there. A being existing in reality as well as in understanding would be greater. We could therefore conceive something greater than the being described as admitting no conceivable superior. This contradicts its defining description. Anselm concludes that it cannot exist only in understanding and must exist in reality.
The key premise is the greatness comparison between existence only in understanding and existence in reality. A second issue is whether the description supplies a coherent concept that the denier genuinely understands. The conclusion follows only if the concept and comparative premise license the contradiction.
An ordinary imagined island does not exist just because we understand its description. Anselm's defender says his premise concerns maximal greatness, rather than every concept. A critic can ask whether adding maximal to a description legitimately changes its existential force. This locates the disagreement more precisely than the complaint that the argument simply imagines God.
If successful, this would be a demonstration independent of uncertain observations. If its disputed premise is rejected, the contradiction does not arise. The argument's a priori status therefore describes its method, not a guarantee that it is sound.
Necessary existence in Proslogion 3
Anselm's chapter 3 develops a stronger claim: God cannot be conceived not to exist. A contingent being can exist or not exist; a necessary being cannot fail to exist. Necessity is not simply lasting a very long time or being impossible for a particular person to destroy.
Anselm argues that a being whose non-existence is inconceivable is greater than one whose non-existence is conceivable. If the greatest conceivable being could be conceived not to exist, a greater being could be conceived whose non-existence is impossible. The greatest conceivable being must therefore have necessary existence.
Chapter 2 contrasts existence in understanding with existence in reality. Chapter 3 contrasts contingent existence with necessary existence. They are related, but collapsing them into the same claim obscures the extra reasoning. Nor is Anselm merely saying God exists because he uses the word necessary: he argues that a being admitting a superior would not be the God described.
The defence gains force against comparisons with ordinary contingent objects: no particular island is something whose non-existence is inconceivable. Yet another question arises. Does understanding the description necessarily existing being establish that any such being is possible, let alone actual? A conditional claim that God, if real, exists necessarily may differ from proving that God is real.
Later modal arguments develop this possibility issue using possible-world reasoning. They should not be silently substituted for Anselm's text. At this stage, the important skill is identifying the distinctive claim and the premise about greatness on which it depends.
What would justify belief?
The ontological argument offers a different kind of justification from an inference based on the world. If its premises are true and the reasoning valid, it would establish its conclusion without needing evidence of design or a first cause. Its appeal is that necessity would avoid the uncertainty of inductive analogies.
A valid argument has a conclusion that follows necessarily from its premises; a sound argument is valid with true premises. A valid reconstruction of Anselm does not settle whether the greatness and existence premises are acceptable. A denier who rejects a premise may be questioning soundness, rather than failing to understand the logic.
The prayerful context can make the argument an exercise of faith seeking understanding. It might articulate why an existing believer takes God to be ultimate. Yet personal coherence and publicly compelling proof are different kinds of justification. An argument offered to a non-believer must explain why its disputed premise should be accepted without first accepting the conclusion.
The relevant comparison with observation concerns those standards. An observational argument has an accessible starting point but may underdetermine its cause. Anselm's argument seeks a necessary result but depends on a disputed concept-to-reality move. Listing the cosmological argument as an alternative does not refute Anselm; one must examine his own inference. Likewise, calling the argument elegant does not prove its premises.
A justified judgement may therefore regard Anselm as a serious account of maximal and necessary being while reserving judgement about real existence. The next lesson tests that inference through Gaunilo and Kant, asking whether their criticisms can be answered without assuming the very existence at issue.