[16] The reason for the use of si is the avoidance of ambiguity. Si is not used with the 1st and 2nd persons, because there is no possibility of ambiguity in these cases.
129. The pronoun "it" is not expressed with impersonal verbs (see par. [164]).
Examples.—Kiu estas tie? Estas mi = Who is there? It is I. Neĝas = It snows. Pluvis = It rained. Necesas, ke oni manĝu = It is necessary to eat.
Possessive Pronouns (Pronomoj posedaj).
130. Possessive Pronouns are formed by adding the adjectival A to the personal pronouns. They are essentially adjectives, and follow the adjectival rules as to the formation of the plural and the accusative.
131. They are mia = my, mine, via = your, yours, thy, thine (cia = thy, thine, like its personal pronoun, ci, is rarely used), lia = his, ŝia = her, hers, ĝia = its, nia = our, ours, ilia = their, theirs, sia = his (own), her (own), hers, its (own), their (own), theirs, one’s (own).
Examples.—Mia patro, via frato, lia fratino, ŝia onklo, kaj iliaj onklinoj, estas en la domo = My father, your brother, his sister, her uncle, and their aunts are in the house. Mi vidis vian libron, lian bastonon, ŝian ombrelon, kaj ilian keston en la stacidomo = I saw your book, his stick, her umbrella, and their box in the station. Mi havas viajn librojn = I have your books. Ĝia koloro estas ruĝa = Its colour is red. Mia fratino renkontis vian fraton kaj viajn amikojn = My sister met your brother and your friends.
132. When a possessive pronoun stands alone, as in sentences like the following, it may or may not be preceded by the article la, at the writer’s option, but many authors prefer to omit the article on the ground that it is superfluous.
Examples.—Ĉar ni ĉiuj havas (or, ĉar ĉiu el ni havas) unu vortaron, prenu (la) vian kaj lasu (la) mian = Since we have each a dictionary, take yours and leave mine. Ŝiaj infanoj estas pli grandaj, ol (la) viaj = Her children are bigger than yours.
Note in the first example that ĉiuj is in the plural because it is in apposition to ni (see par. [69] (c)).