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, seems to have been, in some form or other, a very common one previous to the publication of Reid’s philosophical treatises; although Des Cartes, Arnauld, and most of the Cartesians, Leibnitz, and probably Locke, understood by mental ideas, only modes of the mind itself in their representative capacity. The ideas assailed by Reid were, however, entities distinct from the act of perception, and they were employed to account for our knowledge of the material world, and for the phenomena of memory, imagination, and reasoning. These intellectual phenomena were supposed to have become more intelligible when—on the basis of self-knowledge, and without any critical account of what other notions and beliefs are implied in the ability to observe, experiment, remember, and compare—the existence of such representative images was assumed by the philosopher, in working his theory of knowledge from within the region of the mind outwards, to independent and permanent realities.

The inadequacy of this supposed intellectual machinery to afford an ultimate explanation of knowledge is manifest, especially in two respects. 1. In its opposition to the belief that has been inserted in the structure of our mental constitution, that we have a direct knowledge of the qualities of matter—this hypothesis regarding the understanding as in immediate connexion only with what is representative of these qualities. 2. It is implied that the philosophers who maintain this doctrine, thereby overlook the need, or at least superficially perform the process of a comprehensive inductive exa-