Reasons which it would require too much space to set forth render it probable that all the tense signs are really auxiliary verbs or come from them. This is evident of the optative, as has already been shown. The present only is simple, as it has no tense sign.
Slight differences are found between the personal signs of some tenses, so that these tenses can be distinguished by them, a trait usually seen only in tongues so far cultivated that the grammatical forms have undergone such changes as no longer to present simple and uniform combinations. Equally curious is the regular omission of the tense sign of past time in the third person plural only. Although, except in this case and that of the present, each tense has its definite sign, inserted between the stem and the personal sign, yet there are, besides these, various particles expressing past time, which can accompany the usual tense form, so that there is a double sign of time, one in the word itself and one loosely attached to it.
The languages of the Mbayas, Abipones, Mocobis and Lules are closely allied both in words and in some grammatical forms. It is all the more extraordinary, therefore, to find the last-mentioned pursuing a method in the structure of its verb which is almost totally opposed to that in the other three tongues.
The languages of this class approach in their conjugations those of the more cultivated tongues, in which each verbal inflection has a fixed and independent form. Both the person, the tense and the mode signs are united to the stem, in such a manner that none of the three can be said to be either less or more loosely attached than the others.
All the conjugations about to be discussed lack, however, that fixity of form which grammatically satisfies the mind.
The elements are placed definitely and regularly one by the other, but are not incorporated into each other, and are therefore readily recognizable.
They are found, moreover, outside of the verb elsewhere in the language either without any change or with slight differences of sound; the personal signs as pronouns, the other affixes as particles.
The composition of the verb is separable, and may receive into itself other parts of speech.