Things which have nothing in common cannot be understood, the one by means of the other; the conception of one does not involve the conception of the other.
VI.

A true idea must correspond with its ideate or object.
VII.

If a thing can be conceived as non--existing, its essence does not involve existence.
PROPOSITIONS.
PROP.I.Substance is by nature prior to its modifications.
Proof .-- This is clear from Deff.iii.and v.
PROP.II.

Two substances, whose attributes are different, have nothing in common.
Proof .-- Also evident from Def.iii.

For each must exist in itself, and be conceived through itself; in other words, the conception of one does not imply the conception of the other.
PROP.III.