Anselm made Christian doctrine an occasion for rigorous dialectical inquiry, asking how faith seeking understanding can reason about God, necessity, freedom, and redemption.
Intellectual setting
Anselm wrote in monastic and ecclesiastical institutions before the rise of the medieval universities, drawing on Augustinian and Neoplatonic traditions while facing English royal pressure as archbishop.
Key ideas
That than which nothing greater can be thought
The Proslogion argues that a being understood as unsurpassably great cannot be conceived merely as existing in thought rather than in reality.
Satisfaction and incarnation
Cur Deus Homo explains redemption through the claim that human sin creates a disorder humans cannot repair, requiring a mediator who is both divine and human.
Legacy
His arguments set a durable agenda for philosophy of religion and medieval theology, provoking immediate objections from Gaunilo and later critiques from Aquinas, Kant, and modern logicians.