Given some impulses active others are thereby aroused in the absence of what would otherwise be their necessary stimuli. Such impulses I call imaginative, whether images occur or not, for image-production is not at all essentially involved in what the critic is interested in as imagination. Which other impulses are brought in is in part determined by which were co-operative together originally when all the impulses had their own stimuli, that is to say, in the non-imaginary experiences from which the imaginary experience derives. In so far as this factor comes in the imagination may be said to be _repetitive_. The imagination we are concerned with may be called _formative_[64] by way of distinction. For present circumstances are at least as important. Remember in a changed mood a scene which took place under a strong emotion. How altered is its every aspect! The selection of the impulses which take effect is changed; the impulses are distorted, they run in different courses. The imaginative construction is always at least as much determined by what is going on in the present as by what went on in the past, _pasts_ rather, whence it springs. Many of the most curious features of the arts, the limitation of their number, their formal characteristics and the conditions of impersonality, detachment and so forth, which have given rise to much confused discussion of the ‘æsthetic’ state for example, are explained by this fact. In difficult communication the artist must find some means of so controlling a part of the recipient’s experience that the imaginative development will be governed by this part and not left to the accidents of repetition which will differ naturally from individual to individual. As a basis for every art, therefore, will be found a type of impulse which is extraordinarily uniform, which fixes the framework, as it were, within which the rest of the response develops. These are among the most uniform impulses, among those which come nearest to having a one-one correlation with their stimuli, of all those which we experience. In poetry, rhythm metre and tune or cadence; in music, rhythm pitch timbre and tune; in painting, form and colour; in sculpture, volume and stress; in all the arts, what are usually called the formal elements are the stimuli, simple or complex, which can be most depended upon to produce uniform responses. It is true that these responses are not so uniform as the reflexes, as sneezing or blinking for example. But even these are to a considerable extent subject to interference and modification by impulses of higher levels. What communication requires is responses which are uniform, sufficiently varied, and capable of being set off by stimuli which are physically manageable. These three requisites explain why the number of the arts is limited and why formal elements have such importance.