As examples of the former may be quoted almost all modern achievements. The metric and decimal systems have come to stay. The bicycle, the motor car, and the typewriting machine have undergone successive improvements till finally they have attained to their more or less definite form. We see from this that when inventions have once reached a certain degree of suitability they are not afterwards easily replaced by others. There is, therefore, only one adequate criterion of the stability of an international language, namely, that of suitability or adaptation to its purpose, and we maintain that it is only by means of continuous reforms and improvements that it will succeed in satisfying this criterion and so finally attain to stability. In the work of Couturat and Leau, referred to above, there are described about ten artificial languages which have sprung up during and after the period of Volapük and Esperanto, and in which the experience of their predecessors has been more or less made use of. A study of these attempts leads to the surprising result that they often differ amongst themselves less than, for example, the Romance languages. If, then, one were to choose any one of these languages and to direct its systematic development according to the principles which experience and knowledge have shown to be requisite for the construction of an international language, one would in each case arrive finally at approximately the same result. At the present day the rapid development in every department of life has made us only too ready to regard everything around us as transient. We forget, however, that the rapidly accumulating inventions and discoveries which startle and surprise us always refer to new things. One must bear in mind that there also exist things which in their essential features can _only be invented once_, and that the international language in its final form is one of these. An excellent means of convincing the incredulous is to demonstrate the absence of arbitrariness in the character of an invention or improvement, and the degree of general consent which a given system has already obtained. Whenever one has recognised the natural and logical basis of a discovery one perceives relationships which restrict the ideas of chance and haphazard originally associated with it in one's mind. It is, therefore, quite unnecessary in the case of an international language to be afraid of "the arbitrary action of private persons who possess neither the right nor the authority to introduce reforms into Esperanto," as Dr. Zamenhof has recently stated. One ought rather to feel sure that the best means of defending an international language against arbitrary changes is the degree of its concordance with sound theoretical principles.