Basic contractions: do, da, no, na, pelo, pela

Contractions help express "Pedro's house" or "the teacher's name" naturally in Portuguese. Combinations like a casa do Pedro, o nome da professora, café da manhã (breakfast) and no Brasil (in Brazil) are everywhere. Unlike English, where "of the" stays as two separate words, Portuguese fuses the preposition and the article into one. Skip these contractions and you will sound like you are speaking broken Portuguese by leaving separate words that normally join. These twelve forms (do, da, dos, das, no, na, nos, nas, pelo, pela, pelos, pelas) appear in almost every sentence, making them absolutely essential from your first day.

DE Contractions (of/from + the)

These express possession, origin, and characteristics.

Formation:

• de + o = do (of/from the – masculine singular)

• de + a = da (of/from the – feminine singular)

• de + os = dos (of/from the – masculine plural)

• de + as = das (of/from the – feminine plural)

Common uses:

• Possession: O carro do Paulo (Paulo's car)

• Origin: Ela é do Brasil (She's from Brazil)

Basic Locations

• "Estou no hotel" (I'm at the hotel)

• "O livro está na mesa" (The book is on the table)

• "O gato está no jardim" (The cat is in the garden)

• "Estamos na sala" (We're in the living room)

• "Eles estão nos parques" (They're in the parks)

Simple Possession

• "O livro do aluno" (The student's book)

• "A casa da Maria" (Maria's house)

• "O carro dos pais" (The parents' car)

• "A bolsa da professora" (The teacher's bag)

Contractions with Indefinite Articles

Both expanded and contracted forms are correct in speech and writing; style may favor one or the other:

• Expanded: "em uma casa"

• Contracted: "numa casa"

• Expanded: "de um amigo"

• Contracted: "dum amigo"

Names and Titles

With proper names, the contraction depends on whether the article is used:

• "Casa de Pedro" (no article, no contraction)

• "Casa do Pedro" (with article, must contract)

• "Livro de João" OR "Livro do João" (both correct)

Portuguese contracts more preposition–article pairs than Spanish

Spanish only fuses two preposition–article pairs (a + el = al, de + el = del), so a Spanish speaker can say de la casa without contracting at all. Portuguese has sixteen usual combinations of de, em, por and a with the four forms of the definite article, with a separation rule before an infinitive's subject. That is why learners coming from a Spanish background often forget to contract: their native language only does it in two cases.

Source: Adros Verse — Prepositions in Romance Languages.