At this point light seems to be thrown on the puzzle by the doctrine of Leibnitz,[87] that the only way in which a unity can, without ceasing to be such, contain an indefinite multiplicity is by “representation.” Experience, in fact, presents us with only one example of a unity which remains indubitably one while embracing an indefinite multiplicity of detail, namely, the structure of our experience itself. For the single experience regularly consists of a multiplicity of mental states, both “focal” and “marginal,” simultaneous and successive, which are nevertheless felt as one single whole because they form the expression of a coherent purpose or interest. And this conscious unity of feeling, determined by reference to a unique interest, is the only instance to which we can point when we desire to show by an actual illustration how what is many can at the same time be one. If we can think of the thing’s qualities and the law of their connection as standing to one another in the same way as the detailed series of acts embodying a subjective interest of our own, and the interest itself which by its unity confers a felt unity on the series, we can in principle comprehend how the many qualities belong to the one thing. In that case the thing will be one “substance” as the embodiment of an individual experience, determined by a unique subjective interest, and therefore possessing the unity of immediate feeling. Its many qualities will “belong” to it in the same sense in which the various constituents of an experience thus unified by immediate feeling are said to “belong” to the single experience they constitute. And thus our idealistic interpretation of the general nature of Reality will be found to contain the solution of the problem of Substance and Quality.