Why
This means 'because' and is used to answer a '¿Por qué?' question. It is one word with no accent mark.
This means 'What for?' or 'For what purpose?'. Use it to ask about the goal or intention of an action.
A more literal and slightly formal way to ask 'For what reason?'. It's useful for adding emphasis.
Why do you study Spanish?
I study Spanish because I like Latin music.
My friend is not here. —Why?
What is this button for?
The distinction between '¿Por qué?' (why?) and 'porque' (because) is standard and universal across all Spanish-speaking countries. This is one of the most consistent rules in the language.
The phrase is the same, but you will hear it used with the 'vosotros' form for plural 'you'. For example, '¿Por qué no venís a la fiesta?' instead of the Latin American '¿Por qué no vienen a la fiesta?'
While the phrase itself is identical, the melodic intonation of questions in the Rioplatense dialect can make it sound different to the ear. The pronunciation of the words remains the same.
Writing 'porque' as one word for a question. — Incorrect: '¿Porque no vienes?' Correct: '¿Por qué no vienes?' The question 'why' is always two words with an accent on the 'e': ¿Por qué? The answer 'because' is one word with no accent: porque.
Confusing pronunciation and stress. — In the question '¿Por qué?', the stress is on the second word: por-KAY. In the answer 'porque', the stress is on the first syllable: POR-keh. Mixing these up is a common sign of a beginner.
Using '¿Por qué?' when you mean '¿Para qué?'. — If you ask '¿Por qué compraste un carro?' (Why did you buy a car?), you're asking for the reason or cause. If you ask '¿Para qué compraste un carro?' (What did you buy a car for?), you're asking about its intended purpose (e.g., 'To drive to work').