Final answer:
Plantinga argued in support of Anselm's ontological argument for the existence of God, specifically focusing on the concept of necessary existence. He presented different formulations of the argument to support the reality of the distinction between necessary being and contingent being.
Step-by-step explanation:
Plantinga argued in support of Anselm's ontological argument for the existence of God. The ontological argument, proposed by Anselm in the 11th century, attempts to prove the existence of God based on the concept of necessary existence.
Anselm argued that God is a being whose non-existence is inconceivable, and therefore, God must necessarily exist. Plantinga expanded on this argument and presented various formulations of the ontological argument to support the reality of the distinction between necessary being and contingent being.
Example: Plantinga's modal ontological argument presents the idea that it is possible for a maximally great being (God) to exist in all possible worlds. If this is true, then God must exist in the actual world as well.