1. As expressed independently.
2. As incorporated in the verbal form as an auxiliary verb.
3. As included in the verbal form merely as an idea.
The differences of the languages under comparison can be appreciated most correctly by means of these three headings; but it must not be forgotten that any language may use the first and one of the last two methods, and that in languages which have a substantive verb conjugated with and without auxiliary verbs, all three may be employed.
I.
When the notion of Being is expressed independently.
I must except from this class all instances where the substantive verb is formed from a radical, inasmuch as this root, like any other, must assume the verbal form, and thus come under one of the two other divisions. In such case it expresses the notion of Being, either by an auxiliary, as in the German Ich bin gewesen, or simply in the form, as, I am. When it is remembered that the substantive verbs of all languages are derived from concrete conceptions and impart to these merely the general notion of Being, the above becomes still more obvious.
Now if there is no root-form for the substantive verb, and yet it is expressed independently, and not by another verbal form, this can only be done either by the position of the governing and governed words, or by linguistic elements which are not properly verbs, but only become so by this use. In the former case the substantive verb is merely understood, in the latter it appears in a definite word, but without a fixed radical.
1. When the notion of Being is understood.
One of the most common forms of sentences in American languages is to bring together an adjective and a substantive, the substantive verb being omitted.
Mexican: in Pedro qualli, the Peter (is) good.