Write out and explain the essential points of Descartes's argument that God's existence is included in his essence, otherwise known as the ontological argument.
Strictly speaking, Descartes's version of the ontological argument for God's existence isn't a formal proof but rather a self-evident axiom that is intuitively grasped by the mind. In other words, Descartes's ontological argument is a priori—that is to say an argument whose truth can be established by reasoning that is independent of empirical proof. For Descartes, we know that God exists not by experience but through reasoning.
We can do this because, Descartes argues, we already have the idea of God in our minds, the idea of a supremely perfect being. We are born with this idea; it is innate. Once we understand that this is what God is, we will recognize not just that he exists but that he must exist. In other words, his essence is also his existence.
As the idea of God is innate, there is no need for us to construct any kind of arbitrary definition which would always be vulnerable to the attacks of religious and philosophical skeptics alike. Instead, Descartes's ontological argument relies on an innate idea which he claims is given to each and every one of us.
Furthermore, this is a clear and distinct idea, something that is so self-evidently true that it cannot logically be contradicted. From this idea, the rational mind, unfettered by prejudice, is able to derive, through a process of logical deduction, that necessary existence is contained in the clear and distinct idea of a supremely perfect being (i.e., God).
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