1. There may be languages in which all words, both empty and full, retain their independent form. Even words which are used when we should use mere suffixes or terminations, retain their outward integrity in Chinese. Thus, in Chinese, _jin_ means man, _tu_ means crowd, _jin-tu_, man-crowd. In this compound both _jin_ and _tu_ continue to be felt as independent words, more so than in our own compound _man-kind_; but nevertheless _tu_ has become empty, it only serves to determine the preceding word _jin_, man, and tells us the quantity or number in which _jin_ shall be taken. The compound answers in intention to our plural, but in form it is wide apart from _men_, the plural of _man_. 2. Empty words may lose their independence, may suffer phonetic decay, and dwindle down to mere suffixes and terminations. Thus in Burmese the plural is formed by _to_, in Finnish, Mordvinian, and Ostiakian by _t_. As soon as _to_ ceases to be used as an independent word in the sense of number, it becomes an empty, or if you like, an obsolete word, that has no meaning except as the exponent of plurality; nay, at last, it may dwindle down to a mere letter, which is then called by grammarians the termination of the plural. In this second stage phonetic decay may well-nigh destroy the whole body of an empty word, but--and this is important--no full words, no radicals are as yet attacked by that disintegrating process. 3. Phonetic decay may advance, and does advance still further. Full words also may lose their independence, and be attacked by the same disease that had destroyed the original features of suffixes and prefixes. In this state it is frequently impossible to distinguish any longer between the radical and formative elements of words. If we wished to represent these three stages of language algebraically, we might represent the first by RR, using R as the symbol of a root which has suffered no phonetic decay; the second, by R + ρ or ρ + R, or ρ + R + ρ, representing by ρ an empty word that has suffered phonetic change; the third, by rρ, or ρr, or ρrρ, when both full and empty words have been changed, and have become welded together into one indistinguishable mass through the intense heat of thought, and by the constant hammering of the tongue. Those who are acquainted with the works of Humboldt will easily recognize, in these three stages or strata, a classification of language first suggested by that eminent philosopher. According to him languages can be classified as _isolating_, _agglutinative_,[7] and _inflectional_, and his definition of these three classes agrees in the main with the description just given of the three strata or stages of language.