Por qué, por que, porque and porqué.
The four forms have related meanings but they are not interchangeable. Let´s see:
POR QUÉ (why): preposition por + interrogative or exclamatory qué
It´s used for direct and indirect questions.
Examples:
Direct question: ¿Por qué no fuiste a su fiesta? Why didn´t you go to her party?
Indirect question: No sé por qué no fuiste a su fiesta. I don´t know why you didn´t go to her party.
Exclamatory sentence: ¡Por qué calles más sucias estuvimos!
POR QUE : it has two different uses.
Preposition por + relative pronoun que (it´s very often used with an article)
Esa es la razón por (la) que no fui a su fiesta. That is the reason why I didn´t go to her party
Preposition por + subordinate conjunction que: when a verb, noun or adjective is has to be followed by the preposition “por” and this introduces a subordinate sentence.
Su escuela optó por que las clases terminaran en mayo en lugar de en Junio. Her school opted to finish classes in May rather than in June.
PORQUE: causal or final conjunction.
Causal conjunction (because): it´s used for expressing a cause, reason or motive.
No fui a su fiesta porque estaba enferma. I didn´t go to her party because I was ill.
Final conjunction (in order to, so that): it´s used for expressing a purpose and it´s followed by a subjunctive verb.
Trabajo mucho porque mi hija pueda estudiar. I work a lot in order to my daughter can study.
PORQUÉ: it´s a noun equivalent to cause, reason or motive. It has singular and plural form and it´s usually used preceded by an article.
No entiendo el porqué de tu respuesta. I don´t understand the reason for your answer.
No entiendo los porqués de tu respuesta. I don´t understand the reasons for your answer.
