Every element in a form, whether it be a musical form or any other, is capable of exciting a very intricate and widespread response. Usually the response is of a minimal order and escapes introspection. Thus a single note or a uniform colour has for most people hardly any observable effect beyond its sensory characteristics. When it occurs along with other elements the form which they together make up may have striking consequences in emotion and attitude. If we regard this as an affair of mere summation of effects it may seem impossible that the effect of the form can be the result of the effects of the elements, and thus it is natural and easy to invent ultimate properties of ‘forms’ by way of pseudo-explanation. But a little more psychological insight makes these inventions appear quite unnecessary. The effects of happenings in the mind rarely add themselves up. Our more intense experiences are not built up of less intense experiences as a wall is built up of bricks. The metaphor of addition is utterly misleading. That of the resolution of forces would be better, but even this does not adequately represent the behaviour of the mind. The separate responses which each element in isolation would tend to excite are so connected with one another that their combination is, for our present knowledge, incalculable in its effects. Two stimuli which, when separated by one interval of time or space, would merely cancel one another, with another interval produce an effect which is far beyond anything which either alone could produce. And the combined response when they are suitably arranged may be of quite another kind than that of either. We may, if we like, think of the effects of impulses at various intervals of time upon a pendulum, but this metaphor is, as we have suggested, insufficient. It is over simple. The intricacies of chemical reactions come nearer to being what we need. The great quantities of latent energy which may be released by quite slight changes in conditions suggest better what happens when stimuli are combined. But even this metaphor incompletely represents the complexity of the interactions in the nervous system. It is only by conjecture that its working can as yet be divined. What is certain is chat it is the most complex and the most sensitive thing of which we know.