Q.E.D.
PROP.IX.

The more reality or being a thing has, the greater the number of its attributes (Def.

iv.).
PROP.X.Each particular attribute of the one substance must be conceived through itself.
Proof .-- An attribute is that which the intellect perceives of substance, as constituting its essence (Def.

iv.), and, therefore, must be conceived through itself (Def.

iii.).