ILGUR: Italian Language, Grammar and Usage Resource

Perché is a conjunction that can have two functions in Italian grammar: un valore causale, that corresponds to the English, because, and un valore finale, that corresponds to the English, so that.

When perché has un valore causale,  it is followed by the indicative:

Voglio dormire perché sono stanco.
I want to sleep because I am tired

Un valore causale indicates a cause or a reason, as in the example above — I want to sleep for the very reason that I am tired.

When perché has un valore finale, it isfollowed by the subjunctive:

Vado a casa perché possa domire.
I’m going home so that I can sleep.

Un valore finale expresses an aim, a goal or a purpose — I am going home with the express goal of sleeping.

In writing, affinché is often used to replace perché in order to avoid any ambiguity between the valore causale and the valore finale. There are several other common conjunctions (congiunzioni) that require the subjunctive – you can learn more about them here.

A conjunction is a word that connects sentences, phrases and clauses. The following conjunctions are followed by the subjunctive:

• affinché | so that
• perché (when used with un valore finale) | so that
  
• a meno che…non | unless
• prima che | before
• senza che | without
  
• benché | although
  
• sebbene | although
  
• a condizione che | provided that
  
• purché | provided that
• come se | as if
  With this expression, only the congiuntivo imperfetto or congiuntivo trapassato can be used

Prima che, senza che, and perché or affinché only take the subjunctive when the subjects of the two clauses are different. When they are the same use prima di + infinitive , senza + infinitive, or per + infinitive. Consult the following examples:

Vado al supermercato prima che tu parta.
I am going to the store before you leave.

Vado al supermercato prima di partire.
I am going to the store before I leave.

Scrivo l’articolo perché il pubblico capisca i problemi del governo.
I am writing the article so that the public understand the problems of the government.

Scrivo l’articolo per poter comunicare al pubblico.
I am writing the article so that I can communicate to the public.