maintained in their primitive form (Numisii, Papisii, Fusii). Speaking metaphorically, we might say that people avoided pronouncing these names in the same free-and-easy manner as the rest of the language. The law of substitution of Germanic consonants, which is usually taken as the type and model of phonetic laws, presents occasional examples of sounds returned upon. It would, however, be in our opinion a mistake to offer the substitution of the Germanic consonants as a fact that was accomplished at a given moment in the history of the Indo-European languages, and the direction of which can be fixed within the limits of two dates. Substitutions were going on all through the middle ages, as is shown by the manner in which Latin words are written in German, and is still going on, as may be perceived when a Bavarian or a man of Würtemberg talks French. Accustomed by the usage of their own language to a certain way of pronouncing the explosives, they carry the habit everywhere.
As to the origin of this phenomenon, it is hardly credible that a population should have agreed to disfigure the sounds of their language by substituting, according to their whim, hard sounds for soft, aspirates for hard sounds, and soft sounds for aspirates. It is easier to comprehend that an alien people, adopting an Indo-European language, should have brought to it the habits of its native pronunciation. A second substitution of consonants, which proceeded from the south of Germany northward, corresponds probably with a new afflux of foreign population, which, bringing similar habits of pronunciation to an idiom already once transposed, displaced the consonants in a new degree, but still in the same direction. The difference between the High German and the Low German and Scandinavian idioms may be explained in some such way as this.
A fourth and last principle of phonetic changes is that they are effected according to the law of least effort. In view of the causes already considered, the tendency of language is to economize effort, and consequently to replace sounds that exact some degree of energy with weaker sounds. Thus the Latin labials p and b become v in French; some letters cease to be pronounced; and assimilations take place in groups of consonants. If we should listen to a Roman of the second or third century from the foundation of the city, we should probably be surprised at the energy of his pronunciation and the intensity of his articulations. Yet it would be incorrect to take this as a constant rule. The shortening and the softening down of words do not always result in diminution of effort. New groups of consonants are formed in the course of changes, which do not require less expenditure, but sometimes more. Reduction of time is thus often attained at the cost of increase of effort.