Anselm of Canterbury's Proslogion (1078) contains the most discussed philosophical argument in history. In a single chapter of a devotional text, Anselm formulated the ontological argument for God's existence - the claim that the very concept of God as 'that than which nothing greater can be conceived' entails God's actual existence. Nearly a thousand years of philosophical discussion, from Gaunilo and Aquinas through Kant and Hegel to Alvin Plantinga and Graham Oppy, has been organized around this argument. What is less often noted is how thoroughly the Proslogion's philosophical argument is embedded in biblical meditation and prayer.
The Thinker and His Work
Anselm was a Benedictine monk, prior and then abbot of Bec in Normandy, before becoming Archbishop of Canterbury in 1093. He wrote the Proslogion as a devotional exercise - a meditation meant to be prayed as well as thought - and insisted that its argument presupposed faith rather than supplanting it. The full title was originally Fides Quaerens Intellectum (Faith Seeking Understanding), a phrase Anselm took from the Septuagint rendering of Isaiah 7:9 ('unless you believe, you will not understand'). The Proslogion is not an exercise in natural theology in the Enlightenment sense - proving God's existence to skeptics from neutral premises - but an exercise in what Anselm called 'necessary reasons': the exploration of what must be true given the content of faith.
Biblical Texts Engaged
Psalm 14:1 (Psalm 13 in the Septuagint/Vulgate) is the text that gives the Proslogion its interlocutor: 'The fool says in his heart, "There is no God."' The 'fool' (insipiens) of Psalm 14 is not a casual atheist but a practical atheist - one who knows the concept of God but acts as though God does not exist. Anselm argues that the fool undermines himself: to understand the concept 'that than which nothing greater can be conceived' is to understand something real, and to claim that this something exists only in the understanding and not in reality is incoherent, because to exist in reality is greater than to exist only in understanding.
Psalm 51:10 ('create in me a clean heart, O God, and renew a right spirit within me') frames the work's contemplative context. Anselm writes in Psalm-like direct address to God throughout: 'Lord, I am not trying to make my way to your height, for my understanding is in no way equal to that, but I do desire to understand a little of your truth which my heart already believes and loves.' The argument emerges from prayer, not from detached ratiocination.
Isaiah 7:9 in the Vulgate reading ('nisi credideritis, non intelligetis' - 'unless you believe, you will not understand') provides the methodological motto. Anselm's 'faith seeking understanding' is an Augustinian formula, and he acknowledges his debt to Augustine explicitly. Faith is not irrational but is the condition that opens the mind to a level of understanding it cannot reach by reason alone starting from scratch.
Core Argument
The argument of Proslogion II (the core ontological argument) can be reconstructed as follows: God is defined as 'that than which nothing greater can be conceived.' Even the fool who denies God's existence understands this definition - the concept of God is in the fool's understanding. But if God exists only in understanding and not in reality, then we can conceive of something greater - a being that has all the properties of God's concept plus real existence. But that would mean 'that than which nothing greater can be conceived' is not, after all, that than which nothing greater can be conceived - a contradiction. Therefore God must exist in reality.
Proslogion III extends the argument: God not only exists but necessarily exists - it is impossible to conceive of God as not existing, for a being whose non-existence is impossible is greater than a being whose non-existence is possible.
Intellectual Context
Anselm was writing at a moment when medieval theology was beginning to absorb Aristotelian logic (through Boethius and the newly recovered logical works) into the interpretation of Scripture and the Fathers. His method - proceeding by 'necessary reasons' from definitions to conclusions - is the first mature example of scholastic philosophical theology. The Proslogion presupposes the realist metaphysics in which concepts (like 'that than which nothing greater can be conceived') track real natures, not mere mental constructions.
Reception and Critique
Gaunilo of Marmoutiers, a fellow monk, offered the first rebuttal almost immediately: if the argument worked, one could prove the existence of a perfect island by the same logic. Anselm replied that the argument applies only to a being of which none greater can be conceived - uniquely God - and not to finite things. Aquinas rejected the argument in Summa Theologica I.2.1, arguing that even if we grant Anselm's definition, God's existence is not self-evident to us, only to God. Descartes reformulated the argument in the Fifth Meditation. Kant's famous objection - that existence is not a predicate and cannot be included in a concept - dominated discussion from the eighteenth century.
In the twentieth century, Charles Hartshorne and Norman Malcolm rehabilitated the modal version of the argument (the argument from necessary existence in Proslogion III), and Alvin Plantinga developed this into the modal ontological argument using possible worlds semantics: if it is even possible that a maximally great being exists, then such a being actually exists in every possible world, including the actual world. This argument is widely regarded as valid, and the debate has shifted to whether maximal greatness is a coherent concept and whether its possibility can be granted.
Legacy
The Proslogion established the genre of philosophical theology - rigorous argument conducted from within faith - that defined the medieval scholastic enterprise from Anselm through Aquinas, Duns Scotus, and Ockham. Its argument has generated more sustained philosophical discussion than perhaps any other argument in history. The very phrase 'ontological argument' was coined by Kant, but the argument's staying power suggests that Anselm had identified something genuinely puzzling about the relationship between the concept of God and God's existence.
Key Passages
'Lord, I am not trying to make my way to your height, for my understanding is in no way equal to that, but I do desire to understand a little of your truth which my heart already believes and loves. For I do not seek to understand in order to believe, but I believe in order to understand.' (Proslogion I, trans. Ward)
'Therefore, Lord, you who give understanding to faith, give me as much understanding as you know to be fitting, that you are as we believe, and that you are what we believe.' (Proslogion II)
Contemporary Relevance
The ontological argument's modern modal version (Plantinga's) is a live topic in analytic philosophy of religion. More broadly, Anselm's method of 'faith seeking understanding' has been retrieved by Reformed epistemologists (Plantinga, Wolterstorff, Alston) as a model for Christian philosophy: one begins from within the deliverances of faith and seeks to understand their implications and coherence, rather than first establishing God's existence from neutral premises. This approach has transformed philosophy of religion from a primarily apologetic enterprise into a robustly internal theological discipline.