de + os/as = dos/das

The contractions dos and das are essential building blocks to become proficient in Portuguese. The preposition de primarily translates to both 'of' and 'from' in English, which gives learners an immediate mental hook for why dos and das mean both 'of the' and 'from the'. Unlike English, where 'of the' remains two separate words, Portuguese strictly requires this fusion (it is mandatory), unless the article or demonstrative pronoun is part of the subject of an infinitive verb, or the word 'os' or 'as' functions as a direct object pronoun.

1. Formation:
These are simply the plural equivalents of the singular contractions do (de + o) and da (de + a).

• de + os = dos: Used before masculine plural nouns, or when 'os' acts as a demonstrative pronoun.
• de + as = das: Used before feminine plural nouns, or when 'as' acts as a demonstrative pronoun.

2. Primary Uses:

• Possession: To show who something belongs to (e.g., 'O livro dos alunos' - The students' book).
• Origin: Used with countries or groups that require articles (e.g., 'Eles são dos Estados Unidos' - They are from the United States).
• About: Used to indicate the subject matter being discussed (e.g., 'Eles falam dos problemas' - They talk about the problems).
• Time Ranges: Used to indicate the starting point of a time range, especially with hours (e.g., 'Eu trabalho das nove às cinco' - I work from nine to five). Note that the feminine plural word horas (hours) is implied here (e.g., 'das nove [horas]').
• People's Names: In many regions, articles are used before names, leading to contractions (e.g., 'A casa dos Silva' - The Silvas' house). While some traditional grammarians recommend pluralizing the surname to match the article ('A casa dos Silvas'), keeping the surname in the singular ('A casa dos Silva') is extremely common in everyday practice and is accepted or even preferred by modern European Portuguese prescriptive grammar. In Brazilian Portuguese, however, pluralizing the surname ('A casa dos Silvas') is widely accepted and standard.
• Verbs requiring 'de': Many common verbs, like gostar de (to like) or precisar de (to need), must combine with the article of the following noun (e.g., 'Eu gosto das flores' - I like the flowers).
• Quantity/Group: Used to express 'one of the' or 'most of the' (e.g., 'Um dos amigos' - One of the friends, 'A maioria das pessoas' - Most of the people).
• Partitive: Used to express an unspecified quantity or 'some of' a whole (e.g., 'Ele comeu das bolachas' - He ate some of the cookies).
• Superlatives: Used in relative superlative constructions to express 'the [adjective] of the [group]' (e.g., 'O mais alto dos irmãos' - The tallest of the brothers, 'O melhor dos mundos' - The best of the worlds).
• Demonstrative Pronouns: 'Os' and 'as' can function as demonstrative pronouns (meaning 'those' or 'the ones'), which also contract with 'de' (e.g., 'Gosto mais das que comprei ontem' - I prefer the ones I bought yesterday; 'Os meus sapatos e os dos meus irmãos' - My shoes and those of my brothers).

3. The Infinitive Exception:
In formal writing, do not contract if the article or demonstrative pronoun is part of the subject for an infinitive verb. This is because a subject cannot be preceded by a preposition. For example: 'É hora de os meninos comerem' (It is time for the boys to eat) or 'O facto de os que estudam passarem' (The fact that those who study pass). However, in informal, everyday speech, native speakers (especially in Brazil) frequently ignore this rule and use the contracted form anyway (e.g., 'É hora dos meninos comerem' or 'Apesar dos alunos...').

4. The Object Pronoun Exception:
Do not contract 'de' with 'os' or 'as' when they function as direct object pronouns meaning 'them'. For example: 'Tive a oportunidade de os conhecer' (I had the opportunity to meet them). In this case, 'os' is a pronoun receiving the action of the verb, not an article, so they remain separate. Note that this structure is primarily used in European Portuguese; Brazilians would typically use enclisis ('de conhecê-los') or colloquial subject pronouns ('de conhecer eles').

5. Register Note:
Contractions with indefinite articles (like duns/dumas) are grammatically correct and acceptable in formal registers in European Portuguese. However, formal written Brazilian Portuguese shows a strong preference for the uncontracted forms ('de uns/umas').

6. A 'Sticky' Preposition:
The preposition de is highly 'sticky' and also fuses with pronouns, such as dele (de + ele) or deste (de + este).

7. Pronunciation Note:
The 'o' in dos is generally pronounced like a 'u' (/dus/) in Portugal and most of Brazil. English-speaking learners should be careful not to pronounce dos like the English word 'dose'. Additionally, the 's' in both dos and das changes its sound depending on the speaker's dialect and the following word. Crucially, when followed by a word starting with a vowel (like 'dos alunos'), the 's' is pronounced as a /z/ sound.