_All the 'combinations' which we actually know are_ EFFECTS, _wrought by the units said to be 'combined,'_ UPON SOME ENTITY OTHER THAN THEMSELVES. Without this feature of a medium or vehicle, the notion of combination has no sense. "A multitude of contractile units, by joint action, and by being all connected, for instance, with a single tendon, will pull at the same, and will bring about a dynamical effect which is undoubtedly the resultant of their combined individual energies.... On the whole, tendons are to muscular fibres, and bones are to tendons, combining recipients of mechanical energies. A medium of composition is indispensable to the summation of energies. To realize the complete dependence of mechanical resultants on a combining substratum, one may fancy for a moment all the individually contracting muscular elements severed from their attachments. They might then still be capable of contracting with the same energy as before, yet no co-operative result would be accomplished. The medium of dynamical combination would be wanting. The multiple energies, singly exerted on no common recipient, would lose themselves on entirely isolated and disconnected efforts."[173] In other words, no possible number of entities (call them as you like, whether forces, material particles, or mental elements) can sum _themselves_ together. Each remains, in the sum, what it always was; and the sum itself exists only _for a bystander_ who happens to overlook the units and to apprehend the sum as such; or else it exists in the shape of some other _effect_ on an entity external to the sum itself. Let it not be objected that H_{2} and O combine of themselves into 'water,' and thenceforward exhibit new properties. They do not. The 'water' is just the old atoms in the new position, H-O-H; the 'new properties' are just their combined _effects_, when in this position, upon external media, such as our sense-organs and the various reagents on which water may exert its properties and be known. "Aggregations are organized wholes only when they behave as such in the presence of other things. A statue is an aggregation of particles of marble, but as such it has no unity. For the spectator it is one; in itself it is an aggregate; just as, to the consciousness of an ant crawling over it, it may again appear a mere aggregate. No summing up of parts can make an unity of a mass of discrete constituents, unless this unity exist for some other subject, not for the mass itself."[174] Just so, in the parallelogram of forces, the 'forces' themselves do not combine into the diagonal resultant; a _body_ is needed on which they may impinge, to exhibit their resultant effect. No more do musical sounds combine _per se_ into concords or discords. Concord and discord are names for their combined effects on that external medium, the _ear_.