In order that speech may serve its purpose, it is not necessary, as it is not possible, that heard and spoken words should be identical, but it is necessary that when a man utters different words the heard words should be different, and when he utters the same word on two occasions the heard word should be approximately the same on the two occasions. The first of these depends upon the sensitiveness of the ear and its distance from the speaker; we cannot distinguish between two rather similar words if we are too far off from the man who utters them. The second condition depends upon uniformity in the physical conditions, and is realised in all ordinary circumstances. But if the speaker were surrounded by instruments which were resonant to certain notes but not to certain others, some tones of voice might carry and others might be lost. In that case, if he uttered the same word with two different intonations, the hearer might be quite unable to recognise the sameness. Thus the efficacy of speech depends upon a number of physical conditions. These, however, we will take for granted, in order to come as soon as possible to the more psychological parts of our topic. Written words differ from spoken words in being material structures. A spoken word is a process in the physical world, having an essential time-order; a written word is a series of pieces of matter, having an essential space-order. As to what we mean by “matter”, that is a question with which we shall have to deal at length at a later stage. For the present it is enough to observe that the material structures which constitute written words, unlike the processes that constitute spoken words, are capable of enduring for a long time--sometimes for thousands of years. Moreover, they are not confined to one neighbourhood, but can be made to travel about the world. These are the two great advantages of writing over speech. This, at least, has been the case until recently. But with the coming of radio writing it has begun to lose its pre-eminence: one man can now speak to multitudes spread over a whole country. Even in the matter of permanence, speech may become the equal of writing. Perhaps, instead of legal documents, we shall have gramophone records, with voice signatures by the parties to the contract. Perhaps, as in Wells’s _When the Sleeper Awakes_, books will no longer be printed but merely arranged for the gramophone. In that case the need for writing may almost cease to exist. However, let us return from these speculations to the world of the present day.