Archbishop Anselm of Canterbury, driven into exile…

Archbishop Anselm of Canterbury, driven into exile by William II, writes, during these years of church-state struggle, his greatest theological work, Cur Deus Homo (“Why God Became Man”), completed in 1098), presenting theology as "faith seeking understanding" in the form of a dialogue that all readers can easily follow.

In his highly influential Proslogion, Anselm argues that even one who denies the existence of God knows what is meant by the term—namely, "a being greater than which none can be conceived."

As such a notion cannot, according to Anselm, exist only in the mind—for to exist in the mind and in reality is greater than to exist only in the mind—there must necessarily be in reality a being greater than which none can be conceived.

This definition constitutes for Anselm the ultimate ground for all that is believed and taught about God—namely, his unity, his Trinity, his incarnation, and his redemption of humankind from sin.

(Some philosophers view Anselm’s argument as the ontological proof for the existence of God; others reject it as an illicit inference from the mental to the physical order of existence.)