The main fact which differentiates primitive groups among themselves is diversity of language. To this rule the Moï present no exception, for they offer the choice of a considerable number of dialects. There are very nearly as many dialects as tribes, and, what at first seems even more extraordinary, the dialect of one village is usually unintelligible to the inhabitants of any other. But this singularity vanishes when we investigate more closely, and for these reasons.
The development of a language is intimately connected with the simultaneous intellectual and social evolution of the race which employs it. Now the civilization of the Moï has been stationary, if not actually retrogressive, for a prolonged period, and accordingly it is to be expected that their language, far from consolidating itself, should be subject to all the influences which flow from contact with neighbouring populations.
The learned philologist Cabaton has classified the Moï dialects into three broad divisions, according to the degree in which they have been modified by the tongues spoken by neighbouring peoples who have advanced to a higher stage of civilization. These three divisions comprise:
(a) Dialects of Malayo-Polynesian origin.
(b) Dialects of Kmer origin.
(c) Dialects of Thibeto-Birman, Taî or Chinese origin.
This diversity of dialects is responsible for the fact that the word "Moï" has no ethnical sense at all and that it is a mere generic term which, as I have explained before, can conveniently be used to describe the whole complex of barbarous groups which dwell in the mountain uplands of Indo-China. The word does not signify an autonomous entity with clearly defined characteristics, but merely a medley of various elements, of which many have lost all trace of common origin.
It is even more difficult to catalogue the different races which go to make up the inhabitants of Indo-China than to catalogue the dialects. At first sight some of them seem to be pure, but closer inquiry soon dispels the illusion. There are many reasons to account for this, among which may be cited the prevalence of polygamy and the perpetual inter-tribal conflicts in the course of which the vanquished, after a short period, are absorbed by the victors, to the evident advantage of the latter.
If the dialects are innumerable, there is virtually only one method, employed by all the groups, of communicating ideas or transmitting thought. It consists of the use of certain conventional signs. The more common of these are triangular or hexagonal figures of bamboo or rattan, measuring one foot eight inches in their greater dimension and hung in some conspicuous place. These geometrical forms warn the traveller of impending danger or notify a prohibition to cross the boundary of a "taboo" village.
Another method of communication is by means of a string with a series of knots. This practice recalls the quipos which were in use among the Peruvians and Mexicans to record important events and as a medium for the transmission of thought.