DESCARTES: MEDITATION 5
 At long last, the Meditator is ready to ﬁnd out what can be known! In the Second Med-
itation he discovered his own existence (and his nature as a thinking thing) to be indubitable;
in the Third and Fourth Meditations he managed to validate the Clarity-and-Distinctness Rule
by establishing the existence of a non-deceptive Deity, explaining error as the product of the
misuse of the will by letting it outrun the intellect, so to speak. The Meditator now knows that
he too has a non-deceptive nature and, with due caution, that whatever he clearly and distinctly
perceives must be true. And what might that be?
 Now the Fifth Meditation offers one or two new proofs of the existence of God—for free,
it seems, since they aren’t required for the overall argument. (The Meditator may think there
is only one new proof here; it isn’t clear.) The ﬁrst turns on the fact that the Meditator sees
clearly and distinctly that God’s existence is part of God’s essence, or, to put it another way,
that part of what it is to be God is to exist. But this isn’t very convincing, because deﬁnitional
existence doesn’t tell you anything about real existence; if I deﬁne a ‘squond’ as ‘an existing
round square’, then what it is to be a squond involves existence. But there aren’t any such things.
The second proof given here is sometimes known as “Descartes’s Ontological Argument”: God,
by deﬁnition, must contain all perfections; existence is a perfection; therefore, God exists. This
is slightly better, but depends on the obscure claim that existence is a perfection. What would
that mean? One thing is better than another simply because it exists? (Are you better than your
nonexistent twin sibling?) Fortunately, we don’t need these arguments, since we have the proof
in the Third Meditation.
 Far more important is what the Meditator says at the beginning of the Fifth Meditation