Spanish Subjunctive
Sometimes when I'm in the middle of class, or in my free time, I would look at the back of the textbook and read the spanish sections to entertain myself. To my surprise I can understand a good majority of it very well.
I have been learning the Subjunctive for a while but I can't seem to figure out when to use it. There was this one sentence that read "El gobierno ha aprobado legislación antimonopolista para impedir que se formen monopolios y deshacer los que ya existen." You can probably figure out by now this is an Enconomics textbook, Haha. Now, by just reading it, I know what it says but I cannot figure out why it is subjunctive and if there is a straight (as in word for word) and understandable translation for it. My mind wants to figure out if there's a sentence structure rule that tells the sentence to form into the subjunctive or if that's not the case.
If you could provide your answers, that would be great! 
2 Answers
El gobierno ha aprobado legislación antimonopolista para impedir que se formen monopolios y deshacer los que ya existen
Take the subjunctive part in English: "...monopolies are formed..." Is that what the sentence is saying? That monopolies are forming? Not really. The sentence says that that the Government is trying to prevent monopolies from forming, which means that the phrase "monopolies are formed" is only used just to complete the main idea, which is that the Government wants to prevent that formation - that phrase is there only because it supports the main verb, not because it is what you want to express independently. This is the whole point of the Spanish subjunctive: if you need to mention something, but only in order to express a more complex idea, you must use subjunctive. You only use indicative when the phrase is what you want to express regardless of any other parts of the sentence.
The government has passed anti-monopolistic legislation in order to prevent the formation of monopolies and dissolve those which currently exist.
Here, the phrase para impedir que triggers a subjunctive clause. In fact, this type of phrase always does because it references a hypothetical/unfinished event/an abstract idea.
If the phrase said, para impedir que se forman monopolios, it wouldn't make sense because the law would be trying to prevent something that has already happened literally. In the context of this phrase, the formation of monopolies is something to be prevented, not something that has already occurred. It's being spoken of as a non-literal event, or idea.
If you still don't see it clearly, think about it this way: why has the government passed this legislation? In order to prevent monopolies. It's irrelevant whether the monopolies have yet formed because the para que lays out the intention of the verb, probar.
I hope that makes sense. You should read the subjunctive sections in the Reference section as well.
