Cosas varias

* PAST TENSE 
In English, the so-called simple past form, sometimes called the preterite, is a true tense in that its use always places the action in the past.[1] The present perfect form is an aspect that relates the past to the present; it specifies a present state that results from past action, and as such it is a form of present tense even though it makes reference to past action.[2] It canbe altered to move the time that the state is experienced to the past. The other basic form of English verbs is the progressive aspect form, which shows ongoing action; this too can be altered to place the action in the past. English also has two forms, one of them unique to the past, that indicate past habitual action.
* The simple past is formed for regular verbs by adding -d or – ed tothe root of a word. Examples: He walked to the store, or They danced all night. A negation is produced by adding did not and putting the verb in its infinitive form. Example: He did not walk to the store. Question sentences are started with did as in Did he walk to the store? The simple past is used for describing acts that have already been concluded, regardless of whether they tookplace habitually or are viewed as a single occurrence seen as a unit (but not if they are viewed as having occurred continuously). It is commonly used in storytelling.
* The past progressive is formed by using a simple past form of to be (was or were) and the main verb’s present participle: He was going to church. This form indicates that an action was continuously ongoing. By inserting not before themain verb a negation is achieved. Example: He was not going to church. A question is formed by fronting the simple past form of to beas in Was he going?.
* The past habitual can be formed in one of two ways. One construction is formed by used to plus the bare form of the main verb (or, technically and equivalently, by used plus the to-infinitive of the main verb). With an action verb itindicates that something occurred repetitively, as in I used to go there, while with a stative verb it indicates that a state was continuously in effect, as in I used to belong to that club. The used to form can be used whether or not the specific time frame of the action is specified (I used to go there; I used to go there every Friday in June). The negation of this form is exemplified by I used not togo there, although in informal usage I didn't use to go there is frequently heard. The interrogative form Used you to go there? is rare; the informal alternative Did you use to go there? is sometimes heard.
The other past habitual form uses the auxiliary verb would (which has other uses as well). For example, Last June I would go there daily conveys repetitive action. When this form is used, itmust be accompanied by an explicit time frame (so for example I would go there. does not occur unless the time frame has already been specified). This form is negated as inLast June I would not go there daily, and it is made interrogative as in Last June, would you go there daily?.
* The past perfect is formed by combining the simple past form of to have with the past participle form of themain verb: We had shouted. This form conveys that an action occurred before a specified time in the past, so it is actually a "past of the past" tense. A negation is achieved by including not after had: You had not spoken. Questions in past perfect always start with had: Had he laughed?
* The past perfect progressive is formed by had (the simple past of to have), been (the past participleof to be) and the present participle of the main verb: You had been waiting. This form describes action which happened in continuous fashion prior to some time in the past. For negation, not is included before been: I had not been waiting. A question sentence is formed by starting with had: Had she been waiting? If emphasis is put on the duration of an action that continued to the reference...