All perception of extension and extended objects is merely a conscious state. Therefore, they say, all such perception is nothing but a modification of our mind and reveals nothing of the qualities and nature of the objects themselves. Our intellectual knowledge, however, is based on this sense knowledge, and as such must also be illusory. It is all a mental construction, a subjective fabrication. That this would destroy the validity of all our knowledge, must be obvious.
Skepticism is inevitable.
This, however, is inconsistent, because their fundamental position is thus relinquished. One can see no logical reason why it should be restricted to this one fact alone. For them to apply a principle of the mental and ideal order to the real and physical world is, according to their own theory, an illogical and unwarrantable procedure. But would be intellectual suicide. Representative realism is the outcome of empiricism, and empiricism is the philosophic offshoot of science.