hay / hoặc (phân biệt)

English uses "or" for everything, but Vietnamese splits it into two distinct grammatical functions, though the lines can blur in casual speech.

1. Hay (The Question "Or")
Use hay in direct questions where you want the listener to choose between options (A or B?). You also use it for indirect questions or internal debate (meaning "whether A or B"). A common structure for this is có... hay không (whether or not). While traditionally the rule is to use hay only for questions, in everyday spoken Vietnamese, it is very flexible and is frequently used in affirmative statements as well.

2. Hoặc (The Statement "Or")
Use hoặc in declarative statements to list possibilities. It simply states facts, rules, or available options without asking anyone to make a choice. It sounds more formal and is the standard choice for written or official contexts. You can also use the paired structure Either ... Or ... to emphasize "either A or B".

Adding "là"
You can attach the word To Be to both words (hay là, hoặc là) to make them sound slightly softer and more conversational. However, hay là has an additional, distinct usage: when placed at the beginning of a clause, it means "How about...?" or "Why don't we...?" to make a suggestion.

Note: Be careful not to confuse the conjunction hay with its identical twins: the adjective meaning "good/interesting" (as in phim hay) or the adverb meaning "often" (as in Often).