why

used for asking or saying the reason for something

por qué, la razón por la que

• Why do you think that?
• Why not?

Collocations why question · why something

• Why are you so late today?

  ¿Por qué estás tan tarde hoy?

used for introducing a reason or explanation

porque, ya que, dado que

• Why not?
• Why don't you...?

Collocations why question · why something

• Why, I'm glad to see you!

  ¡Por supuesto que me alegro de verte!

used for showing surprise or shock

¡qué!

• Why, what a surprise!

• Why, I didn't know you were coming!

  ¡Qué sorpresa verte aquí!