In some languages certain classes of elements have arisen which may be added in a perfectly formal manner to other fixed roots or elements, with or without slight phonetic modifications of either or both parts. Since this occurs in conformity with fairly fixed rules, the meanings of the resultant combinations are, according to the class of the attached elements used, fairly analogous. Thus in English many verb roots obtain the present participle by the addition of the formal element _ing_, in itself now meaningless, but once, no doubt, a separate root. The process of agglutination may be accomplished in many different ways, any of which may be characteristic of whole groups of unrelated languages. These may be roughly divided first into mono- or oligo-synthetic and polysynthetic. The former very nearly approach the isolating languages, since usually only one element may be added at a time, but the process of addition may be accomplished in any of the ways possible to agglutination. Agglutination includes prefixing, suffixing and infixing in all degrees of complexity and fixity. Thus languages may be spoken of as agglutinative only in a relative sense. Some are much more so than others, both in point of the number of elements which it is possible to add, and their dependence upon one another and the root, denoting a higher or lower degree of inextricability in blending. Many languages are only loosely agglutinative and the component parts of the compounds readily resolve. In others, as in the inflecting languages, the combination is inextricable. Thus under the head of agglutinative we have the merely agglutinative or synthetic, readily resolvable combinations, which are often hardly distinguishable from isolating languages, and the less easily divisible inflectional and incorporating types. Any or all of the three processes of infixing, prefixing and suffixing may be employed in simple agglutinative combinations. In inflectional languages the root is attended by prefixes or suffixes which form inseparable modifiers. At times phonetic changes occur which render the complex unlike the simple joining of its component parts.