The comparative philology of former times mainly occupied itself with the collection of such words in different languages as showed some similarity in sound, and even this phenomenon was not thought worthy of too much attention. It was not before the beginning of the nineteenth century that the scientific importance of the problems here involved were recognized, and it was seen that they called for thorough and exact investigation. First of all, the differences in structure that exist between the various European languages were examined more closely than had been done before, and those languages that were seen to possess a number of characteristics in common were then brought together into one group, which was called the Indo-European family of languages. Next, another group was found, namely that of the Semitic languages, the relationship to each other of which had been recognized long before on account of the greater uniformity in grammar and vocabulary. Indo-European and Semitic were then both classed together by virtue of their being ‘inflecting’ languages, that is to say, they change words not by means of endings only, but also through vowel change within the stem, and have grammatical gender.