Johano, knabo, onklo, pentristo, fisxisto", for the final "n" in
"patron, infanon, birdojn, musojn, kokidon, bildon, fisxojn",
distinguishes these words from the subject.

This use of "n" renders clear sentences that are not clear in English.
"John loves Mary more than George" may mean "more than John loves
George" or "more than George loves Mary." In Esperanto it is quite
clear. "Johano amas Marion, pli ol Georgo" means "more than George loves
Mary," because "Georgo" is the subject of the second (elliptical)
sentence, but "Johano amas Marion, pli ol Georgon" means "more than
John loves George," because the final "n" in Georgon shows this to be
not the subject.

There are cases, however, in which it is not necessary to add "n", the
noun or pronoun being distinguished from the subject in another way.
Examples are found in the first exercise:--"Sur la tero" kusxas sxtono,
"On the ground" lies a stone. "Antaux la pordo" staras arbo, "Before the
door" stands a tree. Notwithstanding their position, "ground" and "door"
are seen to be not the subject, because before them are the words "on,"
"before," which connect them with the rest of the sentence--it is "on
the ground," "before the door." So with other sentences.

The words "on", "before", and others given [in Lesson 26] are called
PREPOSITIONS ("pre" = before). The noun or pronoun which follows them
can never be the subject of the sentence.

Remember, then, that

"N" is added to every noun and pronoun, "other than the subject", unless
it has a preposition before it. [Footnote: (i.). The explanation usually