ir + a/para + Destination

When using the verb ir, you must choose between prepositions based on duration, region, and mode of transport:

• Ir a: Prescriptively used for temporary stays or errands. If you are going to the market and coming right back, use a. It often contracts with definite articles: ao (masculine) and à (feminine), as well as their plural forms aos and às (e.g., Vou aos Estados Unidos - I am going to the United States).
• Ir para: Used for longer durations, moving house, or going somewhere to stay. In Brazilian Portuguese (BP), this is often shortened to pra or pro (and plurals pras or pros), and is used as the default for almost all destinations, regardless of duration. Note that pra can be a contraction of para + a, but it is also used as a simple shortening of the standalone preposition para. Crucially, these shortened forms are strictly informal and colloquial; in formal writing, they must always be written out fully as para, para a, para o, etc.

Zero-Article Destinations:
Many cities and countries do not take definite articles, so the preposition stands alone without contraction (e.g., Vou a Portugal - I am going to Portugal, Vou para São Paulo - I am going to São Paulo, Vou pra Portugal - I am going to Portugal).

Modes of Transportation:
To express how you are traveling, use de for general modes of transport (e.g., ir de carro - to go by car, ir de ônibus/autocarro - to go by bus). However, use a for walking (ir a pé - to go on foot) and horseback riding (ir a cavalo - to go on horseback). Note that ir de pé is also a valid expression, but it means 'to go standing up' (e.g., on a crowded bus), not 'to go on foot'.

Attending Events:
The prescriptive rule is to use a when attending events (e.g., vou à festa - I am going to the party, vou ao show - I am going to the concert). However, informal BP routinely uses pra or em (e.g., vou pra festa - I am going to the party, vou na festa - I am going to the party).

The 'Home' Exception:
When 'casa' refers to your own home, the definite article is usually omitted. In Portugal, you say Vou a casa (I am going home) for a quick trip and Vou para casa (I am going home) to stay. In Brazil, Vou para casa or Vou pra casa (I am going home) is used to stay, but for quick trips home, informal BP frequently uses em (e.g., Vou lá em casa - I am going home). Note that when 'casa' is specified or belongs to someone else, the definite article returns (e.g., Vou à casa do João - I am going to João's house, Vou pra casa da minha mãe - I am going to my mom's house).

The 'Em' Trap:
In informal Brazilian speech, people often say Vou no médico - I am going to the doctor (using no). While common in Brazil, this is considered incorrect in formal grammar for destinations. In fact, informal BP uses 'ir + em' (no/na) for almost any physical destination or errand (e.g., vou no mercado - I am going to the market, vou no banco - I am going to the bank). In European Portuguese, em is rejected for the destination of motion, but it is used to indicate a specific vehicle or means of transport (e.g., ir no autocarro - to go on the bus, ir no voo das 10h - to go on the 10 AM flight).

Using 'Até':
A very common alternative preposition is até (to / as far as). It is frequently used by native speakers (especially in Brazil) to express destination and bypass the a/para/em dilemma (e.g., Vou até o supermercado - I am going to the supermarket).

The 'Ir + Infinitive' Trap:
When going to DO something, do not use a preposition. Connect ir directly to the infinitive (e.g., Vou comer - I am going to eat, NOT Vou a comer).