Final answer:
Anselm's argument explores the distinction between necessary and contingent being, and supports the reality of this distinction through the ontological argument.
Step-by-step explanation:
Necessary Being vs Contingent Being
Anselm's argument revolves around the distinction between necessary being and contingent being. A necessary being is one that exists necessarily, meaning it cannot not exist, while a contingent being is one that exists but could also not exist. In other words, a necessary being is self-existent, while a contingent being depends on something else for its existence.
Anselm's Argument
Anselm argued in support of the reality of this distinction by presenting the ontological argument. This argument starts with the definition of God as the greatest being, and then posits that a being that exists in reality is greater than a being that exists only in the mind. Therefore, if God is the greatest being, He must exist in reality.