Subordinating conjunctions introduce a subordinate clause that depends on another main clause. They do not join two elements that are equivalent, as do the Coordinating Conjunctions, but rather indicate that one idea is placed within another. In Quiero que vengas, que vengas cannot stand alone with the same meaning: it needs the main clause Quiero. These conjunctions create relationships of time, cause, condition, purpose, concession, and comparison, and are a central part of the Oraciones Subordinadas.

When, before it, after it and while place an action relative to another. When can refer to a specific moment or to repetition: I'll call you when I arrive; When I was a child, I lived in Seville. Before it marks an action earlier than another: Close the door before you leave. After it indicates a later action: We go out after the rain ended. While presents two actions at the same time: Study while I cook. These conjunctions organize the sequence of facts within the sentence.

Temporal use of actions

Usage	Explanation
Simultaneous action	You use mientras to talk about two actions that occur at the same time.
Earlier action	You use antes de que to place an action before another.
Later action	You use después de que to indicate that an action occurs later than another.
Action in progress	You use cuando to indicate the moment when something happens.

Because, since and as introduce the motive or explanation of an idea. The subordinate clause answers the question why. Because usually goes after the cause or direct response: I did not go because I was sick. Since and as present a known or evident cause and are usually placed at the beginning of the explanation: Since you have time, help me; As there are no tickets, we stayed home. If the conjunction is removed, the causal relation disappears and the two ideas are left without a clear connection.

Causal use to explain motives

Usage	Explanation
Direct motive	You use porque to give the direct cause of an idea.
Apparent explanation	You use ya que when the cause seems clear or shared.
Formal justification	You use puesto que to present a more formal cause.

If, unless and provided that express a condition for something to happen or to limit an action. If presents the more general condition: If it rains, we won’t go out. Unless introduces an exception that prevents the result unless something else happens: We won't go unless it finishes soon. Provided that marks an acceptable or sufficient condition: I’ll lend you the car provided that you come back early. In these constructions, the subordinate clause sets the requirement that controls the main clause.

Conditional use to set requirements

Usage	Explanation
Basic condition	You use si to express a condition necessary for something to happen.
Restrictive exception	You use a menos que to indicate that something happens only if another thing does not happen.
Permission condition	You use con tal de que to indicate a condition that must be met to accept something.

So that and in order that indicate the objective or intention of an action. The subordinate expresses what is done for: I’m writing to you so that you confirm the time; In order that everyone participates, we will send the program in advance. These forms usually appear when a person acts with a clear purpose. The main idea presents the action, and the subordinate explains the goal that that action seeks to achieve.

Final use to express objectives

Usage	Explanation
Main objective	You use para que when the action is done with a concrete intent.
Formal purpose	You use a fin de que to express an objective with a more careful or formal tone.

Although, though and even though introduce a difficulty, a contrast or an obstacle that does not prevent the result. Although can present a real fact or an admitted condition: Although it rains, we go out. Though and even though tend to sound more formal and also announce a strong contrast: Even though he was tired, he kept working; Even though there was a lot of traffic, he arrived on time. The subordinate clause acknowledges the problem, but the main clause shows that the result remains.

Concessive use to mark contrast

Usage	Explanation
Simple contrast	You use aunque to show that something happens despite an obstacle.
Recognized difficulty	You use pese a que to indicate opposition between the idea and the result.
Formal obstacle	You use a pesar de que to express concession with a more emphatic nuance.

Como, tal como and igual que serve to compare actions, forms or ways of doing something. Como can signal similarity in the way: Do it like I told you. Tal como presents an exact match: They explained it as it was in the book. Igual que expresses equivalence: Run as fast as your sister. These conjunctions connect two actions or two ways of acting to show similarity, model or correspondence. In comparative texts, they often bring the subordinate clause closer to the sense of an example or reference.

Comparative use of similarity

Usage	Explanation
Mode comparison	You use como to compare the way something is done.
Similarity comparison	You use tal como to say that something is the same as another thing in form or manner.
Equality comparison	You use igual que to indicate that two things are very similar.

Many subordinating conjunctions require the subjunctive when the subordinate clause presents an unperformed, desired, doubtful, or future action. Before it, so that, in order that, unless, provided that, even though and although in certain contexts usually require it: I will call you before you leave; I do it so that you understand; I don’t go out unless you call me. With if, the verb changes according to the type of condition: If you come, we go out; If you came, we would go out. When the subordinate clause speaks of a real and known fact, the indicative appears; when it expresses purpose, an uncertain condition or future time relative to the main clause, the subjunctive appears. This relationship between conjunction, certainty, and verb tense is a direct foundation for the Oraciones Subordinadas and for the Modo subjuntivo.

Appearance of the subjunctive with these conjunctions

Idea
You use subjunctive after conjunciones de finalidad when the action expresses an objective.
You use subjunctive after conjunciones de condición when the condition is hypothetical or future.
You use subjunctive after conjunciones de concesión when the fact is presented as possible or not realized.
You use subjunctive after antes de que and hasta que because the action has not happened yet.