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A contraction consists of 2 words combined by omitting 1 or more letters (eg, can't, aren't). An apostrophe shows where the omission has occurred. Contractions are usually avoided in formal writing. |

Two negatives used together in a sentence constitute a double negative. The use of a double negative to express a positive is acceptable, although it yields a weaker affirmative than the simpler positive and may be confusing: Our results are not inconsistent with the prior hypothesis. More direct incentives have produced substantial changes in behavior in the past, although not without adverse consequences. Rheumatologic symptoms were not uncommon in both groups. However, it is not grammatically acceptable to use a double negative to emphasize the negative. In the following example, the double negative conveys the opposite of what is intended.The Less

Verbs may have 1 of 3 moods: (1) the indicative (the most common; used for ordinary objective statements), (2) the imperative (used for requesting or commanding), and (3) the subjunctive. Subjunctive verbs cause the most difficulty; they are used primarily for expressing a wish (I wish it were possible), a supposition (If I were to accept the position… ), or a condition that is uncertain or contrary to fact (If that were true… ; If I were younger… ). The subjunctive occurs in fairly formal situations and usually involves past (were) or present (be) forms. The subjunctive is sometimes used incorrectly, eg, where Less

Although some authorities may still advise the avoidance of split infinitives, this proscription a holdover from Latin grammar, wherein the infinitive is a single word and cannot be split has been relaxed. In some cases, moreover, clarity is better served by the split infinitive. | Less

Tense indicates the time relation of a verb: present (I am), past (I was), future (I will be), present perfect (I have been), past perfect (I had been), and future perfect (I will have been). It is important to choose the verb that expresses the time that is intended. It is equally important to maintain consistency of tense. The present tense is used to express a general truth, a statement of fact, or something continuingly true.He discovered enzymes RNA polymerases that directly copy [not copied] the messages encoded in DNA. For this reason, the present tense is often used to Less

Verbs express an action, an occurrence, or a mode of being. They have voice, mood, and tense. | In the active voice, the subject does the acting; in the passive voice, the subject is acted on. In general, authors should use the active voice, except in instances in which the actor is unknown or the interest focuses on what is acted on (as in the following example of passive voice).He was shot in the abdomen and within 10 minutes was brought to the emergency department. If the actor is mentioned in the sentence, the active voice is preferred over the Less

In the active voice, the subject does the acting; in the passive voice, the subject is acted on. In general, authors should use the active voice, except in instances in which the actor is unknown or the interest focuses on what is acted on (as in the following example of passive voice).He was shot in the abdomen and within 10 minutes was brought to the emergency department. If the actor is mentioned in the sentence, the active voice is preferred over the passive voice. | Less