Within certain types, needless to say, some structures are more likely to be successful than others. Given some definite kind of effect as the goal, or some definite structure already being used, a good deal can of course be said as to the most probable means, or as to what may or may not be added. Lyric cannot dispense with tied imagery, it is clear, nor can we neglect the character of this imagery in reading it. A prose composition has to be longer than a lyric to produce an equal definiteness of developed effect. Poems in which there is much turmoil of emotion are likely to be strongly rhythmical and to be in metre, as we shall see when we come to discuss rhythm and metre. Drama can hardly dispense with a great deal of conjecture and further interpretation which in most forms of the novel is replaced by analysis and explanation, and in narrative poetry is commonly omitted altogether; and so on. But no general prescription that in great poetry there _must_ always be this or that,—deep thought, superb sound or vivid imagery—is more than a piece of ignorant dogmatism. Poetry may be almost devoid even of mere sense, let alone thought, or _almost_ without sensory (or formal) structure, and yet reach the point than which no poem goes further. The second case, however, is very rare. Almost always, what seems structureless proves to have still a loose and tenuous (it may be an intermittent) structure. But we can for example shift the words about very often in Walt Whitman without loss, even when he is almost at his best. It is difficult to represent diagrammatically what takes place in thought in any satisfactory fashion. The impulse coming in from the visual stimulus of the printed word must be imagined as reaching some system in the brain in which effects take place not due merely to this present stimulus, but also to past occasions on which it has been combined with other stimulations. These effects are thoughts; and they in their groupings act as signs for yet other thoughts. The little arrows are intended to symbolise these references to things outside the mind. _Emotions, and Attitudes._