As has been seen, the theory of Incorporation is to express the whole proposition, as nearly as possible, in one word; and what part of it cannot be thus expressed, is left without any syntax whatever. Not only does this apply to individual words in a sentence, but it extends to the various clauses of a compound sentence, such as in Aryan languages show their relation to the leading clauses by means of prepositions, conjunctions and relative pronouns. When the methods are analyzed by which the major and minor clauses are assigned their respective values in these tongues, it is very plain what difficulties of expression the system of Incorporation involves. Few of them have any true connecting word of either of the three classes above mentioned. They depend on scarcely veiled material words, simply placed in juxtaposition. It is probable that the prepositions and conjunctions of all languages were at first significant words, and the degree to which they have lost their primary significations and have become purely formal elements expressing relation, is one of the measures of the grammatical evolution of a tongue. In most American idioms their origin from substantives is readily recognizable. Frequently these substantives refer to parts of the body, and this, in passing, suggests the antiquity of this class of words and their value in comparison. In Maya _tan_ means in, toward, among; but it is also the breast or front of the body. The Mexican has three classes of prepositions--the first, whose origin from a substantive cannot be detected; the second, where an unknown and a known element are combined; the third, where the substantive is perfectly clear. An example of the last mentioned is _itic_, in, compounded of _ite_, belly, and the locative particle _c_; the phrase _ilhuicatl itic_, in heaven, is literally “in the belly of heaven.” Precisely the same is the Cakchiquel _pamcah_, literally, “belly, heaven”=in heaven. In Mexican, _notepotzco_ is “behind me,” literally, “my back, at;” this corresponds again to the Cakchiquel _chuih_, behind me, from _chi_, at, _u_, my, _vih_, shoulder-blades. The Mixteca prepositions present the crude nature of their origin without disguise, _chisi huahi_, belly, house--that is, in front of the house; _sata huahi_, back, house--behind the house. The conjunctions are equally transparent. “And” in Maya is _yetel_, in Mexican _ihuan_. One would suppose that such an indispensable connective would long since have been worn down to an insoluble entity. On the contrary, both these words retain their perfect material meaning. _Yetel_ is a compound of _y_, his, _et_, companion, and _el_, the definite termination of nouns. _Ihuan_ is the possessive, _i_, and _huan_, associate, companion, used also as a termination to form a certain class of plurals.