DESCARTES: MEDITATION 5/6
 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?
 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? (You are 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,
when he proposes to review his ideas to see which are clear and distinct. He identiﬁes two
classes of ideas:
• Ideas having to do with “quantity”: extension (in three dimensions), shape, size, position,
movement and direction (combined in “local motion”), and duration.
• Ideas of things with “true and immutable natures”:
Together these cover “the subject-matter of pure mathematics,” that is, arithmetic and geometry,
understood as the intelligible aspect of physical objects as well as abstract disciplines. And, as the
Meditator notes at the very end of the Fifth Meditation, even the hypothesis that he is dreaming
doesn’t matter to mathematical truth.
 The Sixth Meditation is devoted to the external world—what can be known of material
things. The Meditator reviews the ideas he has of external things and, as noted, he ﬁnds that
their mathematical properties can be clearly and distinctly perceived. But the same is not true of
other sensible properties: colour, heat, taste, and the like. But the real question is whether there
are any material objects at all. The Meditator begins by enunciating a principle that follows
from the Clarity-and-Distinctness Rule:
(P) “Everything which I clearly and distinctly understand is capable of being created by God
so as to correspond exactly with my understanding of it.”
Now (P) has to hold, since otherwise God would be a deceiver: it has to be at least possible for
things to be as they (clearly and distinctly) appear. The question is whether they in fact are as they appear. From (P), the Meditator derives a criterion for “real distinction”:
(RD) If x can be clearly and distinctly understood apart from y, then x and y are distinct things.
I can think of a pizza without thinking of pepperoni, so pizza and pepperoni are distinct things.
More to the point, though, the Meditator notes that he is able to clearly and distinctly under-
stand his own nature as a thinking thing without thinking of the body at all—indeed, without
even knowing whether he is associated with a body. So his mind is really distinct from his body
(if he has one). Later on in the Sixth Meditation we get another reason to hold that mind and
body are distinct, namely the divisibility of bodies and the indivisibilit