318. It is this essential distinction between the sequence of feeling upon feeling for a sentient subject and the relation which to a thinking subject this sequence constitutes--a distinction not less essential than that between the conditions, through which a man passes in sleep, as they are for the sleeping subject himself, and as they are for another thinking upon them--which it is the characteristic of Hume’s doctrine of natural relation in all its forms to disguise. Only in virtue of the presence to feelings of a subject, which distinguishes itself from them, do they become related objects. Thus, with Hume’s exclusion of such a subject, with his reduction of mind and world alike to the succession of feelings, relations and ideas of relation logically disappear. But by help of the phrase ‘natural relation,’ covering, as it does, two wholly different things--the involuntary sequence of one feeling upon another, and that determination of each by the other which can only take place for a synthetic self-consciousness--he is able on the one hand to deny that the relations which form the framework of knowledge are more than sequences of feeling, and on the other to clothe them with so much of the real character of relations as qualifies them for ‘principles of union among ideas.’ Thus the mere occurrence of similar feelings is with him already that relation in the way of resemblance, which in truth only exists for a subject that can contemplate them as permanent objects. In like manner the succession of feelings, which can only constitute time for a subject that contrasts the succession with its own unity, and which, if ideas were feelings, would exclude the possibility of an idea of time, is yet with him indifferently time and the idea of time, though ideas are feelings and there is no ‘mind’ but their succession. If an effect is merely a constantly observed sequence, how can an event be an effect the first time it is observed? Hume evades this question;