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19.4.2 a fim de que so that / in order to
In sharp contrast to French and Italian, french: a fin que / italian: affinché, the corresponding portuguese conjunction a fim de que has a de, what is normally only used for prepositions. A fim que, without de, is considered a galicism, in other words an intrusion of gallego, the language spoken in north-east of Spain, into Portuguese. To see it like that is actually a little bit strange. Gallego is the mother of Portuguese, Portuguese evolved from gallego and therefore it would be more logical to say that a fim de que is wrong, but the Portuguese and brasilians don't agree. (A fim que yields 390 000 results in a google search, between them as well sensitive speakers, journalists, university professors, etc.. However a fim de que yields 22 million results. (Don't forget the quotation marks if you want to verify that. Otherwise you will get any website where these three / four words appear in any order.) Therefore the democratic majority decision has to be accepted, although it is not logical.
A fim de que and para que introduce a subordinate clause that describes a goal or a wish. Following the general norm, the conjuntivo is to be used in the subordinate clause. If we wish something or strive for something, there is a subjective evaluation. We have a positive attitude refering the thing we wish, otherwise we wouldn't wish it.
a fim de que / para so that / in order to
Felipe abriu a porta do carro para que sua namorada entrasse.
Felipe opened the door of his car so that his girl friend could get into the car.
A aluna estudou durante muitas horas a fim de que não reprovasse.
The student learned many hours in order to not fail in the exam.
É necessário que lutemos, a fim de que possamos triunfar.
In order to win, we have to fight.
Farei isso a fim de que entendas.
I do it, so that you understand it.
To a fim de que there is a corresponding preposition, a fim de, and after the preposition we must use a verbal noun, in other words the infinitive, see for more details 18.1.7.
a fim de
Estamos economizando dinheiro, a fim de viajarmos* no final do ano.
We economise money in order to go for a trip at the end of the year.
Eu estudei a fim de tirar a nota máxima, mas isso não aconteceu.
I have studied to get best marks, but that didn't happen.
* viajarmos is infinitivo pessoal, see 12.2.5. From a grammar point of view the infinitivo pessoal has the same syntactical function as the infinitivo and can be used wherever a simple infinitivo can be used.