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 THEORY OF KNOWLEDGE. 173 carefully balanced ; frequently, however, the degree of prob- ability attained is so great that our assent is almost equiva- lent to complete certainty. No one doubts, — although it is impossible for him to "know," — that Caesar conquered Pompey, that gold is ductile in Australia as elsewhere, that iron will sink to-morrow as well as to-day. Thus opinion supplements the lack of certain knowledge, and serves as a guide for belief and action, wherever the general lot of man- kind or individual circumstances prevent absolute certitude. Although in this twilight region of opinion demonstra- tive proofs are replaced merely by an " occasion " for " tak- ing " a given fact or idea "as true rather than false," yet assent is by no means an act of choice, as the Cartesians had erroneously maintained, for in knowledge it is deter- | mined by clearly discerned reasons, and in the sphere of I opinion, by the balance of probability. The understanding [ is free only in combining ideas, not in its judgment con-| cerning the agreement or the repugnancy of the ideas com-j pared ; it lies within its own power to decide whether itf will judge at all, and what ideas it will compare, but it has! no control over the result of the comparison ; it is impossible for it to refuse its assent to a demonstrated truth or a pre-l ponderant probability. In this recognition of objective_atid^ universally valid relations_£xislingjmiongJdeas, whjch the thinking subject, through comparisons j/ol untarily in stituted. _discDvefs-va]id orRnds given, but which it can neither alte r nor demur_to, Locke abandons empTrical ground (cf. p. 155) and approaches the ideaTisls 'bT~tTie Platonizing type. His inquiry divides into two very dissimilar parts (a psychological descrip- tion of the origin of ideas and a logical determination of the possibility and the extent of knowledge), the latter of which is, in Locke's opinion, compatible with the former, but which could never have been developed from it. The rationalistic edifice contradicts the sensationalistic foundation. Locke had hoped to show the value and the limits of knowledge by an inquiry into the origin of ideas, but his estimate of this value and these limits cannot be proved from the a posteriori ox^ of ideas — it can only be maintained in despite of this, and stands in need of sup-