Adverbs indicate such things as why, where, when, and how. Typical adverbs in English are words like “soon”, “here” and “quickly”; adverbial phrases are groups of words used in the same way, such as “on Sunday” or “with compassion”. Likewise, an entire clause —remember that a clause has a subject and predicate— may have an adverbial function:

• John is working so that she will notice him. [why]
• John works wherever we want. [where]
• Joan works after school is out. [when]
• Joan works as rapidly as she can. [how]

Adverbial clauses are introduced by conjunctions, such as para que (so that), antes de que (before), and hasta que (until). The indicative or subjunctive mood may be required in the adverbial clause in Spanish, or an adverbial phrase (preposition plus infinitive) may be used, depending on:

1. Whether there is a change of subject. If no change of subject is involved and a preposition exists which corresponds to the conjunction, that preposition plus an infinitive is normally used, e.g.: He's saving his money so he can buy a car, Ahorra su dinero para poder comprar un coche. [A list of the corresponding prepositions is given below.]

2. The type situation or time in the adverbial clause. In general, if the situation in the adverbial clause is viewed as something hypothetical or anticipated —rather than completed, habitual, or factual— then the subjunctive is required. In contrast, if the adverbial expression deals with something that is viewed as completed, habitual, or factual, the indicative is used. Some adverbial conjunctions by their very nature deal with something hypothetical or anticipated and thus are always followed by the subjunctive; others may take either the subjunctive or the indicative.

Adverbial conjunctions which are ALWAYS followed by the subjunctive (because they always indicate a pending/hypothetical action or state):

Conjunction               Translation         Corresp. preposition 

a fin de que                so that              a fin de 
a condición de que          on the condition     that  
a menos que                 unless  
a no ser que                lest, unless  
antes (de) que              before                antes de 
con tal (de) que            provided that         con tal de 
en caso de que              in case               en caso de 
no sea que / no fuera que   lest, so that ... not (= para no) 
para que                    so that               para 
sin que                     without               sin 

Notes: 1) Where de is given in parentheses above, it is optional; that is, the conjunction before may be expressed as "antes que" or "antes de que"; 2) some students remember the more frequent of these conjunctions using the mnemonic device ESCAPA.

Examples:

• No voy a menos que venga ella.
  I'm not going unless she comes.
• Salgo a la una con tal que se termine todo.
  I leave at 1:00 provided everything is done.
• Trabaja mucho para que vivan bien.
  She works hard so they (can) live well.
• No hago nada sin que lo sepan.
  I don't do anything without their knowing it.

Normally a preposition is used when no change of subject is involved; it is followed by an infinitive, not the subjunctive or indicative. Examples:

• Mi hijo vive para tocar la guitarra.
  My son lives to play the guitar.
• Ganaré antes de salir.
  I'll win before I leave [before leaving.]

Adverbial conjunctions of time:
The following adverbial conjunctions deal with time, and are followed by the subjunctive when they introduce an anticipated situation. If they introduce one which is viewed as completed or habitual, they are followed by the indicative. Of course, if there is no change of subject involved and a preposition is available, typically the preposition is used with an infinitive.

Conjunction        Translation                      Preposition
 
a medida que       as, according as  
cuando             when                             (al = upon) 
dado que           granted that, in case that  
después (de) que   after                            después de 
en cuanto          as soon as  
hasta que          until                            hasta 
luego que          as soon as  
mientras           while  
nada más que       as soon as  
por más ... que    no matter how much, however much  
por mucho que      no mater how much, however much  
siempre que        whenever, every time that  
tan pronto como    as soon as  

Examples:

Por lo general lo hago cuando nos levantamos.
I usually do it when we get up. [Indicative]

Lo haré cuando nos levantemos.
I'll do it when we get up. [Subjunctive]

Siempre me lavo los dientes después que comemos.
I always brush my teeth after we eat. [Indicative]

Me lavaré los dientes después de que comamos.
I'll brush my teeth after we eat. [Subjunctive]

Los alumnos lo repiten hasta que el profesor está satisfecho.
The students repeat it until the professor is satisfied. [Indicative]

Los alumnos lo repetirán hasta que él esté satisfecho.
The students will repeat it until he is satisfied. [Subjunctive]

Trabajamos mientras ellos descansan.
We work while they rest. [Indicative]

Trabajaremos mientras ellos descansen.
We will work while they rest. [Subjunctive]

Other adverbial conjunctions:

Aunque (although, even though, even if). The indicative is used if a fact is involved or the outcome is known; otherwise the subjunctive is used:

• Lo haré aunque no le gusta.
  I'll do it, even though she doesn't like it. [Indicative It is a fact that she doesn't like it.]
• Lo haré aunque no le guste.
  I'll do it, even though she may not like it. [Subjunctive]

De modo que, de manera que (so that; in such a way that). These two expressions are identical. If used similarly to para que (in order that, indicating the purpose of an action), they require the subjunctive; they are used with the indicative if they mean “in such a way that” [followed by the actual result or outcome]:

• Escribe de modo que todos la entienden.
  She writes in such a way [i.e., so clearly] that everyone understands her. [Indicative]
• Escribe de modo que todos la entiendan.
  She writes so that everyone will [might be able to] understand her. [Subjunctive]

Como is followed by the subjunctive if it used to mean “if”, by the indicative if it means “because” [at the beginning of a sentence], and by either the indicative or the subjunctive (depending on hypothetical/future aspect) if it means “how(ever)”:

• Como vayas conmigo, te pago la entrada.
  If you go with me, I'll pay for your ticket. [Subjunctive]
• Como no estás listo, me voy sin ti.
  Since you're not ready, I'll go without you. [Indicative]
• Lo hago como dijiste.
  I'll do it like you said. [Indicative]
• Lo haré como digas.
  I'll do it however you (might) say. [Subjunctive]