In his review of the conceptions of time and space (association by contiguity), Hume had found succession to be a quality of impressions and to be given with them. But that is all that can be said――the relation is one of time order, but not a relation that is necessary. The outer impressions happen to occur thus and thus; they need not have occurred thus, and may never occur in this order again. This temporal order is not by any means a causal order. The idea of cause is that of power transferred, but we have no impression of power. Impressions come as sequences, not as consequences or as powers. Sequences of impressions are the only “matters of fact”; consequences are not “matters of fact.” They must, therefore, be only “relations between ideas” and have no objective reality. From Hume’s point of view this is sufficient to show that cause is not valid and real. To deny that we have the concept of cause would, however, be nonsense. We do have the concept, and how is its psychological origin to be explained? How does the idea arise? It does not originate (1) as an _a priori_ concept, _i. e._ by an analysis of ideas, nor (2) as an outer impression, _i. e._ a sensation, nor (3) as memory, since memories are images of impressions. The idea of cause originates from an inner impression――a strong and lively feeling connected with the imagination. But how does it happen that the feeling is so strong that it makes us believe the idea, with which it is connected, is a reality? The feeling does not arise from a single instance of conjunction of two impressions, but from the conjunction of two ideas repeated many times. _The belief in cause is a feeling originating in the constant conjunction of impressions._ This explains why the ideas that fire will burn, that poison will kill, that water will wet――are so lively. The conjunction occurs many times, and an inner necessity or compulsion arises to imagine the second impression after the first. Given the first idea, we learn to expect the second. Repetition produces nothing new in objects, but it produces in the mind a new feeling to pass from one idea to the idea usually attending it. Necessity exists in the mind and not in the objects. =The Extent and Limits of Human Knowledge.= What remnants of knowledge remain after Hume has applied his destructive criticism? His critics would answer that, if Hume had been consistent, no knowledge whatever would remain. Upon the basis of pure positivism, that all knowledge is composed of impressions and their copies, knowledge is an impossibility. But he introduced an additional element, “relations,” that made knowledge possible because it afforded synthesis and allowed distinctions.