In short

Italian possessives normally come with the article glued in front: not mio libro but il mio libro. They agree with the thing owned, never with the owner - so il suo is both his and her. The one systematic exception is a single family member: mia madre, mio fratello. For “this / that”, use questo and quello, and remember that quello reshapes itself before a noun exactly like the definite article: quel treno, quello studente, quegli amici.

The rule

Possessives

Step 1 - Say the article too. In Italian the possessive is an adjective, not a replacement for the article. The default shape is article + possessive + noun: il mio telefono, la tua casa, i nostri amici, le vostre chiavi. English drops the article (“my phone”); Italian does not. This is the single most frequent beginner error, and it is a hard rule, not a preference.

Step 2 - Agree with what is owned, not with who owns it. The possessive copies the gender and number of the following noun, just like any other adjective from Adjectives: agreement and position. So Anna - a woman - says il mio telefono (masculine, because telefono is masculine) and la mia macchina (feminine, because macchina is feminine).

The consequence learners find hardest: suo / sua tells you nothing about the owner’s sex. il suo telefono = his phone or her phone; la sua macchina = his car or her car. Context decides. If it is genuinely ambiguous, Italian repeats the name (il telefono di Anna).

Step 3 - Treat loro as frozen. loro never changes shape: il loro cane, la loro casa, i loro figli, le loro idee. Only the article in front moves.

Step 4 - Drop the article for ONE family member. With a singular, unmodified noun for a close relative, the article disappears: mio padre, mia madre, tuo fratello, sua sorella, nostro figlio, vostra zia, mio marito, mia moglie, suo cugino.

Three things switch the article back on:

• Plural. i miei fratelli, le tue sorelle, i suoi genitori. One brother is mio fratello; two are i miei fratelli.
• loro. loro is never exempt: il loro fratello, la loro madre. Always.
• Any modification - an adjective, a suffix, a diminutive: il mio fratello maggiore, la mia cara zia, il mio fratellino. Also la mia mamma, il mio papà, which count as altered forms (though mia mamma is heard too).

Step 5 - Use the same forms as pronouns. To say mine, yours, hers, just drop the noun and keep the article + possessive: Questo è il mio libro -> Questo è il mio. (This is mine.) The form still agrees with the noun you left out: Di chi è questa penna? - È la mia. After essere, the article is usually dropped: Questo libro è mio.

Demonstratives

Step 6 - questo = near, quello = far. questo points at what is close to the speaker (here, this one, in my hand); quello points at what is further off (there, that one, over by them). questo is also the “this” of time: questa settimana, quest’anno.

Step 7 - Inflect questo the easy way. Four forms only, like a normal -o adjective: questo, questa, questi, queste. Before a vowel the singular often elides: quest’uomo, quest’idea, quest’estate.

Step 8 - Inflect quello like the definite article. Before a noun, quello copies the il / lo / l’ / i / gli / la / le pattern you learned in Definite and indefinite articles. Ask which article the noun would take, then build the matching form: il treno -> quel treno; lo studente -> quello studente; l’amico -> quell’amico; gli amici -> quegli amici.

Step 9 - Shrink quello back to four forms as a pronoun. When no noun follows, quello stops imitating the article and behaves normally: quello, quella, quelli, quelle. The masculine plural pronoun is quelli, never quegli: Quelli sono i miei amici. (Those are my friends.) Compare the adjective quegli studenti with the pronoun quelli.

Forms & patterns

The possessives - agreeing with the thing owned:

Family members - when the article comes back:

quello before a noun, matched to the definite article:

Adjective vs pronoun - the forms are not the same set:

Examples

Common mistakes

• Mio telefono è rotto. -> Il mio telefono è rotto. The article is obligatory. English deletes it; Italian keeps it.
• La mia madre è insegnante. -> Mia madre è insegnante. One singular, unmodified relative takes no article. But la mia mamma and le mie sorelle are correct - modified and plural bring it back.
• Anna cerca la sua telefono. -> Anna cerca il suo telefono. The possessive agrees with telefono, not with Anna. The owner’s sex is invisible in Italian.
• Quello libro è interessante. -> Quel libro è interessante. Before a noun, quello follows the article pattern: il libro -> quel libro. Full quello only where you would say lo.
• Quegli sono i miei amici. -> Quelli sono i miei amici. quegli exists only in front of a noun. Standing alone, the masculine plural is quelli.

Tips

• quello and bello are the same puzzle twice. Line them up against the article and the pattern is identical: il -> quel / bel, lo -> quello / bello, gli -> quegli / begli, i -> quei / bei. Learn one, you have both.
• A two-word test for the kinship rule: one and plain. One relative, no extras -> no article (mio zio). Break either condition - more than one, or any adjective, suffix, or loro attached - and the article returns (i miei zii, il mio zio americano, il loro zio).
• suo is a trap in both directions. Coming from English you will want to pick the form by the owner’s sex; Italian picks it by the noun. Reading Italian, do not assume il suo means his - it can just as well mean hers, and only the context tells you which.
• Frequency note: quegli is less frequent than quei, because it needs a masculine plural noun starting with s + consonant, z, gn, ps or a vowel - though before a vowel it is completely everyday: quegli amici, quegli occhi. quei and quelle do most of the work. If you are unsure and it is a pronoun, quelli is always right.