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 of mental qualities which, on their own account, very much deserve the attention of psychologists, are likely to be productive of confusion when the term is used metaphysically, inasmuch as many popular principles of common sense are far indeed from having any proper claim to the dignity of ultimate notions and beliefs. Instead of the collected original judgments of the human mind, appeals to common sense are often directed to the prejudices of individuals, which must be analyzed not into the inspirations of the Author of our mental structure, but into the perverseness of him on whom that structure has been bestowed.

The detection of the genuine principles of common sense is therefore the result of an intellectual effort which requires qualities peculiar to the philosopher, and the argument from common sense is no irrational appeal to vulgar feeling. The reflex criticism which distinguishes the primary from the other qualities of matter, and which appropriates the former exclusively to the external world, is an illustration, from the phenomena of perception, of the difference between an intelligent and an unscientific appeal to the ultimate criterion of truth. Analogous illustrations might be quoted, from other provinces of knowledge, of the manner in which prejudice is sifted, by the application of this test, and these also may be made to prove that the purport of the Scottish philosophy is by no means to encourage the mob to carry away the ark of metaphysics.