For how long or How long?

 Someone asked me today in class about the use of 
For how long or How long?
This is the answer:

Back in the nineteenth century someone decided, on the analogy of a language other than English, that it was improper to end a sentence in English with a preposition, even though the language had been doing just that since its beginnings. So we're required to follow a rule in formal written English that says we must put the preposition and its objects in the correct order near the word they modify.
So in formal English we write: "For how long have you been in therapy?"
In colloquial U.S. English we say: "How long have you been in therapy for?"
The particular example you chose has a simpler solution that works in both formal and colloquial English: just omit "for," since "how long" and "for how long" are synonymous: "How long have you been in therapy?"
Most other prepositions in questions can't simply be discarded: "To whom did you give the message?" is formal while "Who did you give the message to?" is standard in spoken U.S. English. Note the nominative case of the pronoun "Who," also colloquial. 

Spanish Explanation / Ahora en Español:

 Algunas indicaciones para diferenciar How long? y For how long? em inglés. Como regla general diremos que las preposiciones en las preguntas informales van al final de la pregunta. En este caso en concreto la mejor solución es usar How long? Ya que significa "¿Por cuánto tiempo? Y es equivalemte a for how long? que queda algo redundante.

Lie / Lay / Lying / Laying (Students' doubts)

Lie is an intransitive verb (one that does not take an object), meaning "to recline." Its principal parts are lie (base form), lay (past tense), lain (past participal), and lying (present participle). [Lie meaning "to tell an untruth" uses lied for both the past tense and past participle, with lying as the present participle.] Lay is a transitive verb (one that takes an object), meaning "to put" or "to place." Its principal parts are lay (base form), laid (past tense), laid (past participle), and laying (present participle). The two words have different meanings and are not interchangeable. Although lay also serves as the past tense of lie (to recline) – as in, "He lay down for a nap an hour ago" – lay (or laying) may not otherwise be used to denote reclining. It is not correct to say or write, "I will lay down for nap" or "He is laying down for a nap." The misuse of lay or laying in the sense of "to recline" (which requires lie or lying) is the most common error involving the confusion of these two words. > Once you lay (put or place) a book on the desk, it is lying (reclining, resting) there, not laying there. > When you go to Bermuda for your vacation, you spend your time lying (not laying) on the beach (unless, of course, you are engaged in sexual activity and are, in the vernacular, laying someone on the beach). > You lie down on the sofa to watch TV and spend the entire evening lying there; you do not lay down on the sofa to watch TV and spend the entire evening laying there. > If you see something lying on the ground, it is just resting there; if you see something laying on the ground, it must be doing something else, such as laying eggs.

AN HORRIBLE OR A HORRIBLE?

Frequently I am asked about if it is "a horrible" or "an horrible". Since I'm checking some Halloween essays and I constantly find this mistake. this is the explanation:

It's "a horrible" because if you say the word "horrible" out loud, then you realize the h  isn't silent. And even if a letter is silent you always say a unless the 1st letter of a word is a vowel.