What verbs do you use to mean "to be" in the sense of "to exist" (as in "To be or not to be") or "to be in a place" (as in "Where are you?" "I'm here")? What about predicate nouns? How does one say "to be a man" or "to be an author"?
In my conlang-in-progress, I divide "to be" into three components:
There are two copulas and a null copula.
1. The null is used for statives; the adjective is conjugated as a verb. Habitual aspect is used for permanent traits.
3d pers -neut. -pauc.- nom.
They (mixed gender, fewer than five) are tall. (I see.)
2. [zeθ] (be) is used for exact identity. It is irregular in person, gender, and number. [zeθ] never takes a reinforcing prefix, but does require a reflexive marker on the subject. The participatory evidential marker usually will apply.
masc.-sing.-composed of iron-man-sing.-acc.
I am Ironman.
3. [kima-] (stand) is used for location and class membership. Class membership requires reflexives and progressive aspect.
fem.-sing.-councilor-neut. (mixed anim.)-pl.-refl.-loc.
neut. (mixed anim.)-pl.-stand-fem.-sing.-pres.-prog.-rep.
‘And is one of the councilors (I hear).
(As can be seen from the glosses, this conlang's features include the following:
1. Agglutinative morphology;
2. Agreement between nouns and following words, as shown by prefixes to the following word;
3. A singular-paucal-plural number system;
4. Three genders, with animates following actual sex;
5. Tense and aspect marking on verb;
6. Evidential marking on verbs;
7. [-bal], referring to composition, as a productive suffix;
8. SOV as the basic sentence structure.)