Latin Grammar Mini-Series | Lesson 4.2 - Understanding the verb "to be" in Latin and the expectations of an intransitive vs. transitive verb

Like many verbs that are very commonly used, the verb “to be” in Latin is irregular. Its forms are:  The infinitive is esse which translates as “To be” Singular               1st) sum →  “I am” 2nd) sumus → “we are” 3rd) es → “you are” Plural 1st) estis → “y’all are/you (p) are/you all are” 2nd) est → “he, she, it is” or “there is”* 3rd) sunt → “they are” *Example: “There is a book you should read,”  If you look at this verb linguistically, the base of sum is es-. You can see this base in the forms es, est, estis and esse.  However, there is a rule in Latin that(!!)  If -s- is followed by a nasal sound -- that is -m or -n -- it becomes su-; thus, sum, sumus, and sunt. The verb “to be” is not only unusual in its formation but also in what grammarians call its “expectation,” in other words, the forms that accompany it or that it predicates. The verb “to be” does not expect a direct object because direct objects receive action and there’s no action in the verb “to be.”  An etymological lesson: The technical term for a verb that does not expect a direct object is “intransitive,” meaning in- “not,” trans- “across,” it- “go”;thus, the verb does not carry action across from a subject to a direct object.  Instead, with the verb “to be” two things are equated. For instance, when you say, “The man is a teacher,” you’re essentially saying “Man equals teacher.” So in place of an accusative direct object the Latin sum expects a nominative predicate. In this case the predicate is nominative because it is being equated with the subject which is nominative. So to go back to our example, “The man is a teacher,” “man” is the subject and “teacher” is the predicate. In Latin this sentence would be vir est magister, where vir is the nominative subject and magister is the nominative predicate. Predicates can be adjectives as well as nouns but in either instance the predicate is nominative.  So one can say, puer est parvus “the boy is small,” or otium est malum, “leisure is evil,” or estis boni “y’all are good,” or if you translate the predicate as a substantive, what we studied before, an adjective functioning as a noun, you could translate it as, “y’all are good men,” or “good people” since masculine gender functions as common gender in Latin. Please note that predicate adjectives agree with the subject in number and gender as well as case whereas predicate nouns agree with the subject only in case because nouns have to maintain their own number and gender. Conversely, adjectives must agree with the noun they go with in number, gender and case.