A primary verb can be marked for tense (walked), person (walks) and in some cases number (is, was, were). Present and past tenses are formed with verb inflection, the other tenses are formed in combination with auxiliary verbs. A finite clause includes a primary verb.
A secondary verb is not marked for tense, aspect, mood, number and person, and it cannot serve as a predicate, nor can it be used in an independent clause. See Nonfinite. (These are sometimes called "reduced verbs".) A nonfinite clause includes a secondary verb.
A non-modal auxiliary can be marked for tense and 3rd person, but it does not have a dictionary meaning. It combines with a lexical verb to form meaning. It uses auxiliary support for questions, negatives and emphasis.
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Writing often involves telling stories. Sometimes we narrate a story as our main purpose in writing; sometimes we include brief anecdotes or hypothetical scenarios as illustrations or reference points in an essay.
Even an essay that does not explicitly tell a story involves implied time frames for the actions discussed and states described. Changes in verb tense help readers understand the temporal relationships among various narrated events. But unnecessary or inconsistent shifts in tense can cause confusion.
Generally, writers maintain one tense for the main discourse and indicate changes in time frame by changing tense relative to that primary tense, which is usually either simple past or simple present. Even apparently non-narrative writing should employ verb tenses consistently and clearly.
Began is past tense, referring to an action completed before the current time frame; had reached is past perfect, referring to action from a time frame before that of another past event (the action of reaching was completed before the action of beginning.)
Are installing is present progressive, referring to an ongoing action in the current time frame (the workers are still installing, and have not finished;) will need is future, referring to action expected to begin after the current time frame (the concert will start in the future, and that's when it will need amplification.)
It is not always easy (or especially helpful) to try to distinguish perfect and/or progressive tenses from simple ones in isolation, for example, the difference between simple past progressive ("She was eating an apple") and present perfect progressive ("She has been eating an apple"). Distinguishing these sentences in isolation is possible, but the differences between them make clear sense only in the context of other sentences since the time-distinctions suggested by different tenses are relative to the time frame implied by the verb tenses in surrounding sentences or clauses.
By the time Tom noticed the doorbell, it had already rung three times. As usual, he had been listening to loud music on his stereo. He turned the stereo down and stood up to answer the door. An old man was standing on the steps. The man began to speak slowly, asking for directions.
In this example, the progressive verbs had been listening and was standing suggest action underway at the time some other action took place. The stereo-listening was underway when the doorbell rang. The standing on the steps was underway when the door was opened. The past perfect progressive verb had been listening suggests action that began in the time frame prior to the main narrative time frame and that was still underway as another action began.
If the primary narration is in the present tense, then the present progressive or present perfect progressive is used to indicate action that is or has been underway as some other action begins. This narrative style might be used to describe a scene from a novel, movie, or play, since action in fictional narratives is conventionally treated as always present. For example, we refer to the scene in Hamlet in which the prince first speaks (present) to the ghost of his dead father or the final scene in Spike Lee's Do the Right Thing, which takes place (present) the day after Mookie has smashed (present perfect) the pizzeria window. If the example narrative above were a scene in a play, movie, or novel, it might appear as follows.
By the time Tom notices the doorbell, it has already rung three times. As usual, he has been listening to loud music on his stereo. He turns the stereo down and stands up to answer the door. An old man is standing on the steps. The man begins to speak slowly, asking for directions.
In this example as in the first one, the progressive verbs has been listening and is standing indicate action underway as some other action takes place. The present perfect progressive verb has been listening suggests action that began in the time frame prior to the main narrative time frame and that is still underway as another action begins. The remaining tense relationships parallel those in the first example.
In all of these cases, the progressive or -ing part of the verb merely indicates ongoing action, that is, action underway as another action occurs. The general comments about tense relationships apply to simple and perfect tenses, regardless of whether there is a progressive element involved.
It is possible to imagine a narrative based on a future time frame as well, for example, the predictions of a psychic or futurist. If the example narrative above were spoken by a psychic, it might appear as follows.
By the time Tom notices the doorbell, it will have already rung three times. As usual, he will have been listening to loud music on his stereo. He will turn the stereo down and will stand up to answer the door. An old man will be standing on the steps. The man will begin to speak slowly, asking for directions.
In this example as in the first two, the progressive verbs will have been listening and will be standing indicate ongoing action. The future perfect progressive verb will have been listening suggests action that will begin in the time frame prior to the main narrative time frame and that will still be underway when another action begins. The verb notices here is in present-tense form, but the rest of the sentence and the full context of the narrative cue us to understand that it refers to future time. The remaining tense relationships parallel those in the first two examples.
In general the use of perfect tenses is determined by their relationship to the tense of the primary narration. If the primary narration is in simple past, then action initiated before the time frame of the primary narration is described in past perfect. If the primary narration is in simple present, then action initiated before the time frame of the primary narration is described in present perfect. If the primary narration is in simple future, then action initiated before the time frame of the primary narration is described in future perfect.
The present perfect is also used to narrate action that began in real life in the past but is not completed, that is, may continue or may be repeated in the present or future. For example: "I have run in four marathons" (implication: "so far... I may run in others"). This usage is distinct from the simple past, which is used for action that was completed in the past without possible continuation or repetition in the present or future. For example: "Before injuring my leg, I ran in four marathons" (implication: "My injury prevents me from running in any more marathons").
Inappropriate shifts from past to present, such as those that appear in the above paragraph, are sometimes hard to resist. The writer becomes drawn into the narrative and begins to relive the event as an ongoing experience. The inconsistency should be avoided, however. In the sample, will should be would, and rise should be rose.
This writer uses the present tense to describe the appearance of a dragonfly on a particular July morning. However, both past and future tenses are called for when she refers to its previous actions and to its predictable activity in the future.
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Since acute abdomen requires accurate diagnosis and treatment within a particular time limit to prevent mortality, the Japanese Society for Abdominal Emergency Medicine in collaboration with four other medical societies launched the Practice Guidelines for Primary Care of Acute Abdomen that were the first English guidelines in the world for the management of acute abdomen. Here we provide the highlights of these guidelines [all clinical questions (CQs) and recommendations are shown in supplementary information].
A systematic and comprehensive evaluation of the evidence for epidemiology, diagnosis, differential diagnosis, and primary treatment for acute abdomen was performed to develop the Practice Guidelines for Primary Care of Acute Abdomen 2015. Because many types of pathophysiological events underlie acute abdomen, these guidelines cover the primary care of adult patients with nontraumatic acute abdomen.
A total of 108 questions based on 9 subject areas were used to compile 113 recommendations. The subject areas included definition, epidemiology, history taking, physical examination, laboratory test, imaging studies, differential diagnosis, initial treatment, and education. Japanese medical circumstances were considered for grading the recommendations to assure useful information. The two-step methods for the initial management of acute abdomen were proposed. Early use of transfusion and analgesia, particularly intravenous acetaminophen, were recommended.
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