PROP. IX.————
tion of the effect to be explained. To derive our perceptions of material things from material things, is to derive them from a source in which they are not contained, and which is therefore not competent to impart them. Such is the substance of the revolution effected by Des Cartes on this the standard opinion in the common schools of philosophy; and the downfall of the hypothesis of Physical Influx was the result.
Consequences of the Cartesian correction.7. The Cartesian reform was followed by important consequences. The question now arose—What, then, is the cause of our knowledge; from whence do we derive our cognitions of external objects? If material things and the organs of sense do not originate them,—what originates them? Their efficient cause, answers Des Cartes, their true source, is the power and will of the Deity, who, containing within Himself every perfection, is competent to produce and to impart to us perceptions, or whatever else he may be pleased to produce and to impart.
Scepticism and Idealism arise.8. This solution gave a new turn to the discussion. Now scepticism in regard to the existence of material things broke loose. Now the question emerged—What proof is there that matter exists at all? So long as material things were held to be the causes of our perceptions, a sufficient guarantee