The possessive form of nouns is made by adding an apostrophe and s, ('s); thus, day's, lady's, girl's, clerk's.

To plural nouns ending in s add only an apostrophe; thus, days', ladies', girls', clerks'.

When plural nouns do not end in s, their possessive forms are made by adding the apostrophe and s, the same as singular nouns, thus:

90. In words which end with a sound that resembles that of s, the apostrophe with s forms an additional syllable. Thus:

The only exception to the rule occurs when the addition of another s would make too many hissing sounds, then we add the apostrophe alone. Thus:

91. In forming the possessive of compound nouns, the possessive sign is always placed at the end, thus: