Where do the grammar forms 'I have done' [Present Perfect} and 'I am doing' [Present Continuous] come from?
554134
They are very old, go back to pre-Old English times, even used to be common Germanic usage, but German e.g. has abandoned the present continuous.
1006994
I don't really understand your question.  Do you mean from past tense to present or from a simple sentence to a complex one or what?  Please add details.
1127943
The various proposed answeres are wrong when they suggest that 1 and 3 are incorrect. they are not common, and most people don't now use them, but they have been used in speech and in writing.\n\nEnglish verb tenses, particularly the complex ones (with the helper verbs), are numerous and often only subtly different. In this case the distinction is between a fact of reality (it can't have been <whatever> which would presumably be discovered when actually confronting the facts  and a conditional conclusion disproved. \n\nHis igorance in 1 is the fact,  and the door's locked condition is the fact in 3. For 2 and 4 some investigation suggests that it ould have been impossible that <whatever> because of something which turned up later. It turned out that he knew in 2, while something shows that contrary to expectation, some new fact shows that the door being locked is impossible. \n\nSome languages, like Navajo, include in verb tneses information about  the nature of the agent which caused the <whatever> we are observing. One tnese for a fence knocked down by a windstorm, another for the same fence, knocked down to the same condition, by a living agent (cows, maybe). Englich complex tenses tend to convey information about probabilities and expectations as well as time values and conditionality (eg, subjunctive). for those who master them, the English tense system is a supple and graceful tool.
943124
its very important you understand the difference between "has had" and "have had".  its confusing, but if you dont learn the difference, you'll probably struggle on other little things, and end up never really being fluent.  \n\n"have had" is a past-tense possession term.\n"has had" is a present-tense possession term.\n\n"he has had to go up and down these stairs 9 times today!"\n\n"at the end of the day he will have had 9 chances to drop this package off"\n\n"how many ice cream cones have you had today?"\n "i will have had 3 ice cream cones today."\n\n(often times one will be eating the 3rd ice cream cone while they say it this way.  otherwise, if you had already had 3 ice cream cones that day, and werent already eating another one, you'd say "i had 3 ice cream cones"  but you can say it either way. )\n\n"i have had many chances in my life to do whatever i want"\n\n"look at all the toys you have had!"
773825
http://www.longman.com/ae/azar/grammar_ex/message_board/archive/articles/00179.html\n\nhttp://www.edufind.com/English/grammar/ING3.cfm
548680
"knew" is "know" in the past tense. Since "did" is already in the past tense, no need to repeat it twice.\n\nSame with every verb: I didn't go (not didn't went)\nI didn't swim (not didn't swam)
947082
"Did play" is the  verb. Did (past of do) is part of the verb phrase, or predicate along with "play."  Kim is the subject, and soccer is the direct object which receives the action of the verb. \n\nHope this helps.\n\nSue
754603
I'd advice you to ignore, frankly, some of the advice you've been given on this thread. The four options you put forward are in the following tenses: (1) simple past; (2) present perfect; (3) past perfect; (4) future perfect. Hence, the present perfect of the sentence is "Norman has studied algebra".
209026
A gerund verb occurs in the second and third person present tense and is used to describe an action that happens in the present or to describe an action that was happening in the past in the reflective.\n\nTo give you an example:\n\nVerb: Run\nGerund: running\n\n2nd person present tense: He is running now.\n3rd person present tenst: I am running now.\n\n2nd person reflective (past present tense): He was running when his phone rang.\n3rd person reflective (past present tense): I was running when my phone rang.
271747
Present:\nI am\nyou are\nhe/she/it is\nwe are\nyou all/they are\n\nPast:\nI was\nyou were\nhe/she/it was\nwe were\nyou all/they were\n\nFuture:\nI will be\nyou will be\nhe/she/it will be\nwe will be\nyou all/they will be\n\nPresent Perfect:\nI have been\nyou have been\nhe/she/it has been\nwe have been\nyou all/they have been\n\nPast Perfect:\nI had been\nyou had been\nhe/she/it had been\nwe had been\nyou all/they had been\n\nFuture Perfect:\nI will have been\nyou will have been\nhe/she/it will have been\nwe will have been\nyou all/they will have been
451904
After present tenses! Lol
1177241
the first one was in past tense and the other one is in past progressive tense\nthe meaning is the same. the difference is how the sentence was constructed
900657
The present tense is used for things that are either 1. regular habits or 2. always true.  For example: I wake up at 8am everyday.   The earth is round.  \n\nThe past tense is used to answer things that happened in a known or specific time.  For example: I went to the movies last week.  \n\nHowever, the question you are asking seems to be part of a poem or lyric.  Without further context, it would be impossible to ascertain who the people are or what they are doing.
186597
It's a shame the asker didn't include more of the surrounding text from this article so it could be analyzed more closely.  \n\nAnyhow, grammarians will concur that the structure:  \n\n"...active surveillance and robust peer intervention among high-risk groups such as female sex workers had had an impact in the South..." ,\n\nIS, technically, correct.  Sacramento Dweller was correct in identifying this seemingly awkward grammatical structure as a matter of tense.  Sentences utilizing this particular structure generally fall under the category of "Conditional Sentences."  Sentences featuring the 'had had' syntax are classified as "The Third Conditional," or "Conditional Type Three," and can generally be diagnosed by analyzing them for similarities with following structural formulae:\n\n(The Type 3 Conditional / Third Conditional Formula:)\n\n" IF + <insert past perfect tense verb> + <insert perfect conditional tense verb> = RESULT OF SUPPOSED CONDITIONS.*\n\n*~NOTE:  RESULT(S) of the supposed conditions usually resemble one of the following two structures, depending on when events occurred:  \n\n(1.) Result:  <insert simple present or past tense verb to express an obvious, or predictable fact / outcome>\n\n(2.) Result:  <insert modal verb  + simple present or past tense verb to express a known fact / outcome >\n\nEXAMPLE #1:  "If you had had proper training as an assassin, we would not be in this situation..."\n\nEXAMPLE #2:  "If I'd had proper training as an assassin, you probably wouldn't be here to complain."\n\n(Notice how in EXAMPLE #2, the contractions 'I'd' is used instead of saying, 'I had had' to illustrate the terms of the condition being discussed, though still allowing the reader to ascertain and understand the time-frame and sequence in which events occcurred?)\n\nRules for proper usage of the "Third Conditional / Conditional Type 3" sentence structure state that the structures are 'to be used when talking about unreal, or "hypothetical" situations occurring in the past.'  That means, the related events DID NOT 'ACTUALLY' HAPPEN in the past.  Sentences utilizing this structure are almost always phrased to reckon, "If circumstances were different, what could / would have this been like?"  \n\nThe expression of time / tense in this [third] variety of conditional sentence structure IS identified as the past, and indicates that an action was completed "in" the past.  The condition and / or result, therefore, cannot logically be fulfilled because the action in the "IF" clause never actually happened.  Action in "Third Conditional / Conditional Type 3" sentence structure is almost ALWAYS characterized by the quality of being absurd, and impossible to achieve.\n\nTense and Terminology?\n\n-Simple Present Tense:  Expresses a fact, habit/routine, or ability.\n\n-Simple Past:  Implies that the action happened before and is not happening anymore.\n\n-Past Perfect (Pluperfect) Tense:  Relates that an action or event ended prior to another action or event.\n\n-Present Perfect (Continuous) [Past-composite] Tense:  Indicates either events in recent past, or events which occurred in the past at an unknown time.\n\n-Perfect (Conditional) Tense: Relates varying degrees of certianty or uncertainty about events in recent past, or events which occurred in the past at an unknown time.\n\n-Modal Verbs:  incorporated with other verbs to illustrate the notion of possibility, impossability, necessity or other degree of probability.
379436
In response to your first question, the use of the word "their" in this case is quickly becoming colloquially acceptable in replacement of "his or her" or "your."  This has always been an awkward point in the English language.\n\nIn the second case, the use of "since" implies that the action is still taking place, but the use of "were" implies that the action has been completed.  Therefore, if these cultures still exist and are agricultural, "have been" is correct.  If these cultures no longer exist, then "since" must be eliminated in favor of something more clear.
992937
Well, "go" and "went" are two different forms of the verb "to go".  "I go" is simple present, whereas "I went" is simple past.\n\nBelow I have document uses for both.\n\n"Simple Present"\nUse 1\nUse the Simple Present to express the idea that an action is repeated or usual.  \n\nUse 2\nThe Simple Present can also indicate the speaker believes that a fact was true before, is true now, and will be true in the future. It is not important if the speaker is correct about the fact. It is also used to make generalizations about people or things.\n\nUse 3\nSometimes speakers use the Simple Present to express the idea that an action is happening or is not happening now. This can only be done with Non-continuous Verbs and certain Mixed Verbs.\n\n"Simple Past"\nUse 1\nUse the Simple Past to express the idea that an action started and finished at a specific time in the past. Sometimes the speaker may not actually mention the specific time, but they do have one specific time in mind.\n\nUse 2\nWe use the Simple Past to list a series of completed actions in the past. These actions happen 1st, 2nd, 3rd, 4th...\n\nUse 3\nThe Simple Past can be used with a duration which starts and stops in the past. A duration is a long action often used with expressions like "for two years," "for five minutes," "all day" or "all year."\n\nUse 4\nThe Simple Past can also be used to describe a habit which stopped in the past. It can have the same meaning as "used to". To make it clear that we are talking about a habit we often use expressions such as "always," "often," "usually," "never," "...when I was a child" or "...when I was younger" in the sentence.\n\nI believe that covers all uses of both forms of the verb tenses.  I hope this is what you were looking for.
1059877
"Be did?" This is interesting. Wish I could understand what it means.