When we try to detect some common principle in our various judgments as to whether a thing is one thing or several, the following results seem to emerge:—(1) A thing is clearly not made _one_, as is sometimes assumed, by the possession of an unbroken contour or an uninterrupted temporal existence. The succession of my mental states may make up one mental life, and again my organism from the cradle to the grave may be pronounced in some sense one, though no one can prove that there are no gaps in their temporal existence. Again, even if we leave out of account the corpuscular theories of body according to which every thing that looks to us like a spatially continuous whole with an unbroken contour is really composed of discrete particles with interstices between them, it is abundantly clear that common sense regards as one thing the parts of a system which works as a connected whole, quite independently of the existence or non-existence of immediate contact between them. (2) Again, the unity of the one thing does not depend upon identity of material, whatever that phrase may mean. My organism still remains one thing, though its material is constantly changing by the loss of some elements and the acquisition of others. (3) On the positive side, it is clear that the unity we attribute to one thing is that of teleological structure. A thing is one or many according to the point of view from which you look at it, _i.e._ according to the idea or purpose in the light of which you study it. That is one thing which functions as one, in other words, which is the systematic embodiment of a coherent scheme of structure. Thus, when we are considering the whole of an organism as subservient to the realisation of a unique individual aim or interest, the organism is necessarily judged to be one, because in respect of that interest it behaves as a whole; when we are studying the specific mode of reaction of a particular nerve, for instance, the same organism just as naturally appears to us a multiplicity of distinct but interconnected things. Similarly, a system of material particles appears one thing to us so long as our interest in the system is directed to those ways in which it behaves as one, _e.g._, the exchanges of energy between it and other systems external to it. Generally we may say that whatever is called one is called so because it is the systematic expression of a single aim or interest. A thing, in fact, is one just in so far as it has the character we ascribed, in our last chapter, to a finite individual. Its unity is never _merely_ numerical, but always qualitative, the unity of coherent structure.