English Language Guide: Contraction

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A contraction is the shortening of a word, syllable, or word group by omission of internal letters. In traditional grammar, contraction can denote the formation of a new word from one word or a group of words
An informal type of contraction occurs frequently in speech and writing, in which a syllable is substituted by an apostrophe and/or other mode of elision, e.g., can't for "cannot", won't for "will not". Such contractions are often either negations with not or combinations of pronouns with auxiliary verbs, e.g., I'll for "I will". At least one study has sought to analyze the category of negative informal contractions as the attachment of an inflectional suffix.
Informal speech sometimes allows multiple contracted forms to pile up, producing constructions like wouldn't've for "would not have". Another stereotypically informal contraction is ain't, for "am not" or "is not".
A commonly used English contraction of two words that does not fall into either of the above categories is let's, a contraction of "let us" that is used in forming the imperative mood in the first-person plural (e.g., "Let's go [somewhere]"). Use of the uncontracted "let us" typically carries an entirely different meaning, e.g., "Let us go ". "Let us" is rarely seen in the former sense and "let's" is never seen in the latter one.
Informal contractions are, by their nature, more frequent in speech than writing, e.g., John'd fix your television if you asked him. Contractions in English are generally not mandatory as in some other languages. It is almost always acceptable to write out (or say) all of the words of a contraction, though native speakers of English may judge a person not using contractions as sounding overly formal. Let's, as mentioned above, is an exception to this rule. Another exception is the use of contractions with not in questions: Don't you like it? but not Do not you like it?
Common single-word contractions include: St for "Saint" (in proper names), ma'am for "madam", St meaning "Street" is sometimes given a full point to eliminate any confusion with "Saint". Forms like gov't (or govt) for "government" and int'l (or intl) for "international" are purely written contractions.
Writers of English commonly confuse the possessive form of the pronoun it with its compounded contractions. The possessive form (its) has no apostrophe, while the contraction of it is or it has does have an apostrophe (it's). The same is true of the possessive form of "you" (your) with its contraction you're for "you are".
The linguistic function of contractions is similar to and overlaps that of portmanteau words. Some forms of syncope may also be considered contractions, such as wanna for want to, gonna for going to, and others common in colloquial speech.
Contractions may perform the same function as abbreviations. Strictly, an abbreviation is formed by omitting the ending of a word, for which a full stop (period) is substituted, e.g., Lieut. for "Lieutenant". Contractions omit the middle of a word, and are generally not terminated with a full point, e.g., Ltd for "Limited". However, US style uses more points than British style does, e.g., commonly, in Jr. instead of Jr for "Junior".