7.2 Substitution of the possessive adjectives by de + ele /ela / eles / elas
We put aside the question whether the construction de + ele / ela / eles / elas complies with the standard or normative grammar. It is a matter of fact that this construction is very common. This construction is useful, because it is more precise than the possessive pronouns seu, sua, seus, suas,that can refer to a man or a woman, to a group of men and a group of women.
É a sua casa.
possible meaning:
This is his house.
3. singular, masculine
This is her house.
3.singular, feminine
This is their house.
3 plural, masculine
This is their house.
3 plural, feminine
The problem is that in all roman languages the gender and number of the possessive pronoun, possessive adjective is determined by the the thing possessed and not by the possessor. Therefore the gender and number of the possessor get lost.
This ambiguity can be avoided by contruction with de + ele / ela / eles / elas.
É a casa dele.
3. singular, maskuline
É a casa dela.
3. singular, feminine
É a casa deles.
3. plural, maskuline
É a casa delas.
3. plural, feminine
Substitute in the following sentences the ambiguous possessive adjective / pronouns by de + ele - ela - eles - eles. Which form is to be used is indicated, 3rd person singular masculine for instance is ele. In the case of the 2nd person singular we have to use você (de você).