Page:History of Modern Philosophy (Falckenberg).djvu/244

 222 THEORY OF KNOWLEDGE. stantiality is to be denied to immaterial as well as to material beings. The points in Locke's philosophy which seemed to Hume to need completion were different from those at which Berkeley had struck in. The antithesis of rational and empirical knowledge is more sharply conceived ; the combination of ideas is not left to the choice of the understanding but placed under the dominion of psycho- logical laws; and to the distinction between outer and inner experience (to the former of which priority is conceded, on the ground that we must have had an external sensation before we can, through reflection, be conscious of it as an internal phenomenon), there is added a second, as important as the other and crossing it, between impressions and ideas, of which the former are likewise made prior to the latter. Everyone will acknowledge the considerable difference between a sensation actually present (of heat, for instance) and the mere idea of one previously experienced, or shortly to come. This consists in the greater force, liveliness, and vividness of the former. Although these two classes of states (the idea of a landscape described by a poet and the perception of a real one, anger and the thought of anger) are only quantitatively distinct, they are scarcely ever in danger of being confused — the most lively idea is always less so than the weakest perception. The'actual, outer or inner, sensations may be termed impressions; the weaker images of memory or imagination, which they leave behind them, ideas. Since nothing can gain entrance to the soul except through the two portals of outer and inner experience, there is no idea which has not arisen from an impression or several such ; every idea is the image and copy of an impression. But as the understanding and imagination variously com- bine, separate, and transpose the elements furnished by the senses and lingering in memory, the possibility of error arises. A hidden^_and,_jtherefore mor e dan gerous_ sp,urce of error consists in th e^ reference of an idea to a different impression tha n the one of which it is the cop y. The con- cepts substance and, causality are examples of such fajse reference. The combination of ideas takes place without freedom, in a purely mechanical way according to fixed rules, which in