| Bob, in this case, is a proper noun.
It, in the other case, is a personal pronoun. Generally, nouns can go from the nominative (subjective) case to the independent genitive (possessive) case by adding an apostrophe. If a word ends in "s", then the apostrophe goes after that "s". If the word does not end in "s", then you add an apostrophe, followed by an "s" after the end of the word. A pronoun is treated differently than a proper or common noun when being used in its genitive case. Pronouns have declension (inflection) that can change their endings so they become different words. For example, we can decline the pronouns to show possession using any of these cases: Accusative (objective) case / Possessive Adjective case / Genitive (possessive) case me / my / mine you / your / yours it / its / its her / her / hers him / his / his us / our / ours them / their / theirs Case 1.* "The dog belongs to _" Case 2. "This is _ dog". Case 3. "That dog is _". In all of these cases, a pronoun does not take an apostrophe, unlike you would see with common/proper nouns. Note that this can apply to more than just the noun, in the case of "The Queen of England's dress", where Queen does not take the |