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PROPOSITION VIII.
THE EGO IN COGNITION.
The ego cannot be known to be material—that is to say, there is a necessary law of reason which prevents it from being apprehended by the senses.
DEMONSTRATION.
The ego is known as that which is common to all cognitions, and matter is known as that which is peculiar to some cognitions (Prop. VII.) But that which is known as common to all cognitions cannot be known as that which is peculiar to some cognitions, without supposing that a thing can be known to be different from what it is known to be,—which supposition is a violation of the law of contradiction (see Introduction, § 28). Therefore the ego cannot be known to be material, &c.
Or, again: Matter, in its various forms, is known as the changeable, contingent, and particular element
