33. Up to the present time these same objections might have been urged with equal force against Monism. Indeed, although many philosophers have rejected the two-clock theory of Leibnitz, they have gained a very hesitating acceptance for their own hypothesis of identity. To most minds the difficulty of imagining how a physical process could _also_ be a psychical process, a movement also be a feeling, seemed not less than that of imagining how two such distinct Agents as Matter and Mind could co-operate, and react on each other, or move simultaneously on parallel lines. Although for many years I have accepted the hypothesis of Monism, I have always recognized its want of an adequate reply to such objections. Unless I greatly deceive myself, I have now found a solution of the main difficulty; and found it in psychological conditions which are perfectly intelligible. But knowing how easily one may deceive one’s self in such matters, I will only ask the reader to meditate with open-mindedness the considerations now to be laid before him, and see if he can feel the same confidence in their validity. 34. One of the early stages in the development of Experience is the separation of Self from the Not-Self. I look out on “the vast extern of things,” and see a great variety of objects, included in a visible hemisphere. All these objects in various positions, having various forms and colors, I believe to be wholly detached from, and in every way unallied to, Myself. And what is that Self? It is my Body as a visible and tangible object, separated from all other visible and tangible objects by the constant presence of feelings connected with it and its movements, and not connected with the other objects. This constant presence of feelings is referred to a Soul, which I then separate from my Body, as an Inner Self; and from this time onwards I speak of the Body as _mine_, and learn to regard it in much the same light as other outer objects. In my naïve judgment the external objects are supposed to exist _as_ I see and touch them, whether I or any one else see and touch them or not: they in no sense belong to the series of feelings which constitute the Me. And since my Body resembles these objects in visible and tangible qualities, and also in being external to my feelings, it also takes its place in the objective world. Thus arises the hypothesis of Dualism which postulates a _Physis_, or object-world, and an _Æsthesis_, or subject-world: two independent existents, one contemplated, the other contemplating.