If the availability of his past experience is the first characteristic of the poet, the second is what we may provisionally call his normality. So far as his experience does not tally with that of those with whom he communicates, there will be failure. But both the sense in which it must tally and the sense in which the artist is normal need to be carefully considered. Within racial[61] boundaries, and perhaps within the limits of certain very general types,[62] many impulses are common to all men. Their stimuli and the courses which they take seem to be uniform. At the same time there are many other impulses which are not uniform. It is difficult to give instances, since there are so few names for impulses, but sounds are fairly uniform while words used in isolation are fairly ambiguous stimuli. Impulses could, if we knew enough, be arranged in an order of general uniformity or stability. Some impulses remain the same, taking the same course on the same occasions, from age to age, from prehistoric times until to-day. Some change as fashions change. Between the two extremes are the vast majority; neither, when the nervous system is vigilant, very fixed nor very erratic; set off by a given stimulus and taking the course they do because other impulses are also active or have just been active. For successful communication a number of impulses with their effective stimuli must be common to the communicators, and further the general ways in which impulses modify one another must be shared. We evidently cannot expect that many total situations and responses will have been common, and it is not necessary that they should be. Within limits the disparities can be overcome by what is called imagination. There is nothing peculiarly mysterious about imagination. It is no more marvellous than any other of the ways of the mind. Yet it has so often been treated as an arcanum that we naturally approach it with caution. It is desirable at least to avoid part of the fate which befell Coleridge,[63] and our account will be devoid of theological implications.