Possessive case, defined; rules for forming possessives of nouns; when used.
"Practical Grammar and Composition"
Thomas Wood
Their and theirs are the possessives likewise of they, when they is the plural of it, and are therefore applied to things.
"A Grammar of the English Tongue"
Samuel Johnson
Own is added to possessives, both singular and plural, as my own hand, our own house.
"A Grammar of the English Tongue"
Samuel Johnson