单数they是they或它的词形变化形式（例如them或their）的用法，用于指单独一个人，作为单数形式。

典型地，这种情况出现于不确定的性别，例句：

 "Everyone returned to their seats."
 "Somebody left their umbrella in the office. Would they please collect it."
 "If a person doesn't want to go on living, they are often very difficult to help."
 "The patient should be told at the outset how much they will be required to pay."
 "But a journalist should not be forced to reveal their sources."

类似地，这种情况也可以应用于派生词，例如themself或themselves。

这种用法的一个原因是英语没有专用于不确定性别的单数人称代词。
有些情况，这种用法可以被解释为一种名义约定，因为如everyone之类的单词，虽然在语法上是单数形式，但事实上却是复数的意义。
这种用法逐渐变多的一个原因可能是20世纪的性别包容语言运动，但是它已经被有影响力的作家使用了好几个世纪。

虽然单数they的用法历史悠久，并且在日常英语中广泛使用，但是这种用法从19世纪末开始还是一直受到批评，并且大家的认可度也不同。

词形变化形式与物主代词

单数they与“正常”的複数they有相同的词形变化形式，即them和their。它们通常都使用相同的动词形式，也就是说“when I tell someone a joke they laughs”是不规范的。

反身代词themselves有时也被使用，但是还有一个可选的反身代词形式themself。虽然themself有历史悠久并且在20世纪80年代復活了，但是它还是依然较少使用，并且只被少数人认可。 它在指代性别不明的单个人的时候有时使用，因为这时候複数形式themselves看起来不协调，例如
 "It is not an actor pretending to be Reagan or Thatcher, it is, in grotesque form, the person themself."—Hislop (1984);引自 Fowler's
单数themself在加拿大联邦法律文本中被系统化地使用，用于区别于複数themselves。
 "Where a recipient of an allowance under section 4 absents themself from Canada [...]"—War Veterans Allowance Act, section 14.
 "[...] the following conditions are imposed on a person or group of persons in respect of whom a deposit is required: [...] to present themself or themselves at the time and place that an officer or the Immigration Division requires them to appear to comply with any obligation imposed on them under the Act."—Immigration and Refugee Protection Regulations, section 48.

用法

知名作家的一些老旧用法
早在14世纪的中古英语，they就一直被用于单数形式。 在许多知名作家的著作中都能看来这种用法，包括杰弗里·乔叟、威廉·莎士比亚、简·奥斯丁、威廉·梅克比斯·萨克雷和萧伯纳：
 "And whoso fyndeth hym out of swich blame,
 They wol come up . . ."
—Chaucer, The Pardoner's Prologue (c. 1395); 引用自Jespersen在《Merriam-Webster's Concise Dictionary of English Usage》。
 " Tis meet that some more audience than a mother, since nature makes them partial, should o'erhear the speech."— Shakespeare, Hamlet (1599);引用自《Merriam-Webster's Concise Dictionary of English Usage》。
 "If a person is born of a . . . gloomy temper . . . they cannot help it."— Chesterfield, 《Letter to his son》 (1759);引用自《Fowler's》。
 "Now nobody does anything well that they cannot help doing"— Ruskin, 《The Crown of Wild Olive》 (1866);引用自《Fowler's》。
 "Nobody in their senses would give sixpence on the strength of a promissory note of the kind."— Bagehot, 《The Liberal Magazine》 (1910);引用自《Fowler's》。
 "I would have every body marry if they can do it properly."— Austen,  《Mansfield Park》 (1814);引用自《Merriam-Webster's Concise Dictionary of English Usage》。
 Caesar: "No, Cleopatra. No man goes to battle to be killed."
 Cleopatra: "But they do get killed"
—Shaw,  Caesar and Cleopatra (1901);引用自《Merriam-Webster's Concise Dictionary of English Usage》。
 "A person can't help their birth."— W. M. Thackeray, Vanity Fair (1848);引用自《Merriam-Webster's Concise Dictionary of English Usage》。

同时，除了使用they，使用代词he作为（据称的）性别中性代词也被认可，如下所述：
 "Suppose the life and fortune of every one of us would depend on his winning or losing a game of chess."— Thomas Huxley, A Liberal Education (1868);引自Baskervill.
 "If any one did not know it, it was his own fault."— George Washington Cable, Old Creole Days (1879);引自Baskervill.
 "No one shall be arbitrarily deprived of his nationality nor denied the right to change his nationality."— Article 15, Universal Declaration of Human Rights (1948).
在威廉·梅克比斯·萨克雷的著作中，两个都出现过：
 "A person can't help their birth."—Rosalind in W. M. Thackeray,  Vanity Fair (1848);引用自《牛津英语词典》于Curzan在《Gender Shifts in the History of English》。
与
 "Every person who turns this page has his own little diary."— W. M. Thackeray,  On Lett's Diary (1869);引用自Baskervill, 《An English Grammar》。
并且威廉·卡克斯顿写道：
 "Eche of theym sholde . . . make theymselfe redy."— Caxton,  《Sonnes of Aymon》 (c. 1489)
alongside
 "Who of thise wormes shall be byten, He must have triacle; Yf not that, he shall deye."— Caxton,  《Dialogues in French and English》 (c. 1483).

19世纪的性别通用he的趋势
在非正式英语中使用he而非they的用法的倡导，可以在18世纪中叶找到，在的《A New Grammar》中写道：

1895年的语法（Baskervill, W.M.与Sewell, J.W.的《An English Grammar for the Use of High School, Academy and College Class》）标记了单数they的通用的用法，但是推荐用性别通用he，基于数协议：

Baskervill给出了知名作家的使用单数they的一些例子，包括
 "Every one must judge according to their own feelings."— Byron, Werner (1823), quoted as "Every one must judge of [sic]  their own feelings."
 "Had the Doctor been contented to take my dining tables as any body in their senses would have done . . ."— Austen, Mansfield Park (1814); 
 "If the part deserve any comment, every considering Christian will make it to themselves as they go . . ."— Defoe, The Family Instructor (1816); 
 "Every person's happiness depends in part upon the respect they meet in the world . . ."— Paley, 
但是他更喜欢使用he：
—Baskervill,  An English Grammar

1850年，英国议会通过了一个法案，其中说了，在议会的法案中使用的时候“阳性词必须被视为包括女性”。

据称的性别中性的he的用法直到至少20世纪60年代还能用，虽然有一些he的用法后来因笨拙或愚蠢而被批评，例如指代：
 两性的不确定的人：
 "the ideal that every boy and girl should be so equipped that he shall not be handicapped in his struggle for social progress . . ."— C.C. Fries,  American English Grammar, (1940).
 两性的已知的人：
 "She and Louis had a game—who could find the ugliest photograph of himself."— Joseph P. Lash,  Eleanor and Franklin (1971)
 或者明显可以假设为女人的不确定的人：
 ". . . everyone will be entitled to decide for himself whether or not to have an abortion."— Albert Bleumenthal,  N.Y. State Assembly (1975).

据称的性别中性的he的当代用法

当代著作在指代性别通用或不确定的前面出现的词的时候，有时还是可以看到使用he。
有时指代的人几乎可以确定为男的，例如
 "The patient should be informed of his therapeutic options."— 关于前列腺癌的文本 (2004)
有时前面出现的词指代的人很可能只是男的或者这种职业传统上只有男性人员：
 "It wouldn't be as if the lone astronaut would be completely by himself." (2008)
 "Kitchen table issues . . .  are ones the next president can actually do something about if he actually cares about it. More likely if she cares about it!"— Hillary Rodham Clinton (2008)
还有其它情况，前面的词可能指代：
 一个不确定的人，两个性别都有可能：
 "Now, a writer is entitled to have a Roget on his desk."—Barzun (1985); quoted in Merriam-Webster's Concise Dictionary of English Usage
 "Theyre going to appoint a new manager. Well I hope he does a better job than the present one."
 "A Member of Parliament should always live in his constituency."
甚至在2010年，还是可以发现性别通用he的建议：
 " . . . 当不定代词在前面使用时，需要一个单数的主格、宾格与物主代词 . . ."
 "Everyone did as he pleased" . . .
 "在非正式口语中，复数代词经常被用于当前面的词不确定的时候。但是这种结构现在一般不合适用于正式发言或者书面上。
 非正式： Somebody should let you borrow their book.
 正式： Somebody should let you borrow his book."
 —Choy, Basic Grammar and Usage

20世纪开始趋于使用性别中性语言
在20世纪的下半个世纪，女权主义者关注“性别歧视主义”的男性导向式语言。不但包括man性别通用，而且包括he作为性别通用代词。

争论点是he不能明智地作为性别通用代词，包括男人与女人。
William Safire在他的《纽约时报》的 On Language 专栏上赞同了性别通用he，提及口诀“男性包罗女性”。
Brooklyn的C. Adendyck对《纽约时报》写了一个回复：

1980年，运动受到广泛支持，许多组织，包括绝大多数出版社，都发行了性别中性语言的使用指南。

用于特定的知名人士
在一些情况，可能知道个体但却用they来指代，因为性别未知或者因为他/她偏爱使用they，例如社会媒体应用，可能允许账号持有者来选择非常规性别例如性别酷儿或双性别和一个代词，包括他们可能愿意使用的they/them。

当代用法

自从20世纪60年代以来，在书面语和口语中使用阳性通用名词和代词的频率就在一减少。20世纪90年代在澳大利亚收集的自发讲话语料库中，单数they变最频繁使用的通用代词。单数they的使用上升的原因，至少是部分原因，是性别中性语言的使用的增长。一百年前的作者用he作为不确定性别的指代时可能没有顾虑，但是如今的作者经常会感觉这么用不自在。在正式场合的一种方案通常是写he or she或者其它类似的，但是过度使用这种方式感觉很别扭，或者感觉很政治正确，或者都有。

当代用法中，单数they常被用于指定性别不确定的先行词，至少有一些人这么用，例如当先行词的性别或数量不确定、未知或未揭露的时候。
例子包括不同类型的用法。

用作指代代词先行词

单数先行词可以是一个代词，例如everybody、someone、anybody或者疑问代词例如who：
 先行词为everybody、everyone等等：
 "Everybody was crouched behind the furniture to surprise me, and they tried to. But I already knew they were there." Garner提供的例子。
 "Everyone promised to behave themselves." Huddleston等人提供的例子。
 "Everyone returned to their seats." Pinker提供的例子。
  先行词为nobody或no one：
 "Nobody was late, were they?" Swan提供的例子。
 "No one put their hand up." Huddleston等人提供的例子。
 "No one felt they had been misled." Huddleston等人提供的例子。
 先行词为somebody或someone：
 "I feel that if someone is not doing their job it should be called to their attention." —— 一份美国的报纸（1984），Fowler引用。
 先行词为anybody或anyone:
 "If anyone tells you that America's best days are behind her, then theyre looking the wrong way." 乔治·布什总统, 1991年国情咨文; quoted by Garner
 "Anyone can set themselves up as an acupuncturist."——Sarah Lonsdale "Sharp Practice Pricks Reputation of Acupuncture." 《观察者》1991年12月15日，Garner引用。
 "If anybody calls, take their name and ask them to call again later." Swan提供的例子。
 甚至在性别已知或者可以假定的情况下：
 "Under new rules to be announced tomorrow, it will be illegal for anyone to donate an organ to their wife." Ballantyne, "Transplant Jury to Vet Live Donors", 《星期日泰晤士报》（伦敦）1990年3月25日，Garner引用。 (1990年，妻子可以假定为女性)
 先行词为疑问代词：
 "Who thinks they can solve the problem?". Huddleston等人提供的例子， 《剑桥英语语法》（The Cambridge Grammar of the English language）。

用作指代通用名词先行词

单数先行词也可以是一个名词，例如person（个人）、patient（病人）或student（学生）：
 先词先为名词（例如person、student或patient），泛称使用（例如表示这个类型中的任意一位成员的含义的时候，或者笔者不知道指定的某一个成员）
 ". . . if the child possesses the nationality or citizenship of another country, they may lose this when they get a British passport." 来自英国护照申请表，Swan引用。
 "cognitive dissonance: "a concept in psychology [that] describes the condition in which a person's attitudes conflict with their behaviour"——《麦克米伦商业管理学词典》（Macmillan Dictionary of Business and management） (1988年版)， Garner引用。
 "A starting point would be to give more support to the company secretary. They are, or should be, privy to the confidential deliberations and secrets of the board and the company.— Ronald Severn. "Protecting the Secretary Bird". 《金融时报》，1992年1月6日，Garner引用。
 先行词代表前面提及的一类人的泛称，并且是单数形式
 "I had to decide: Is this person being irrational or is he right? Of course, they were often right."——Robert Burchfield，《美国新闻与世界报道》（U.S. News & World Report），1986年8月11日，《韦氏简明英语用法词典》（Merriam-Webster's Concise Dictionary of English Usage）引用
甚至指代的一类人是已知性别的，有时也用they
 "I swear more when I'm talking to a boy, because I'm not afraid of shocking them" 引自一个访谈
 "No mother should be forced to testify against their child".
 They也可以用于混合性别的先行词：
 "Let me know if your father or your mother changes their mind." Huddleston提供的例子。
 "Either the husband or the wife has perjured themself."这里themself被部分人接受，themselves似乎不那么被接受，himself是不可接受的。Huddleston等人提供的例子。
 甚至对于确定的已知性别的已知的人，they也可以用于忽略或隐藏性别。
 "I had a friend in Paris, and they had to go to hospital for a month."（确定的人，但没指明身份）
 themself一词有时也被使用：
 "Someone has apparently locked themself in the office."[接受度值得怀疑]

有些人比其他人有更大的被接受度，在某些情况下尝试用（形态上）单数代词来替换they会得到荒唐的结果，可以用上面的例子验证。

可接受性和​​规范性指导

虽然性别通用he和性别通用they作为单数代词使用有很长的一段历史了，并且它们至今都依然还在使用中，但是它们还是一直被部分人群系统化地避免使用。
防止表述偏袒任何一方的风格指引有时建议把这些通用的表达重新表述为复数形式来避免被任何一方指责。

单数they的使用在英国英语中比在美国英语中更加被广泛接受 or vice versa. 

一性用法指引我们接受被建议they的单数用法并不是仅仅是用于语义复数的单数词例如everyone，而且也用于前面指代的不确定的“个人”，这些用法的例子甚至常出现在正式演讲中。例如，Casey Miller和Kate Swift，在《无性别歧视写作手册》（The Handbook of Non-Sexist Writing）， Ronald Reagan引用：
 "You must identify the person who has the power to hire you and show them how your skills can help them with their problems."

美国使用指南Garner's Modern American Usage (2003)推荐小心使用单数they，并且尽可能避免使用，因为这么用有点别扭。
 "如果名词–代词不一致性可以避免，尽量避免。如果不可以避免，尽可能小心使用，因为有人会怀疑你的文化水平 . . .".
Garner认为单数they的使用在英国英语中的接受度更大一些：
 "美国英语使用者比英国英语使用者更不能接受这种变化，美国人觉得不确定的they已经是越来越不标准化。"
并且美国英语使用者显然抵制这种变化:
 "它让许多有文化的美国人望而却步，这不幸地对问题的最终解决方案造成了障碍。"
他将使用单数they和everyone，anyone和somebody等先行词的趋势视为不可避免的:
 "尽管这些发展对纯粹主义者来说可能令人不安，但它们是不可逆转的。 语法学家所说的一切都不会改变它们。"

In the 14th edition (1993) of The Chicago Manual of Style, the University of Chicago Press explicitly recommended use of singular use of they and their, noting a "revival" of this usage and citing "its venerable use by such writers as Addison, Austen, Chesterfield, Fielding, Ruskin, Scott, and Shakespeare."
From the 15th edition, this was changed. In Chapter 5 of the 16th edition, now written by Bryan A. Garner, the recommendations are:
 "The singular they. A singular antecedent requires a singular referent pronoun. Because he is no longer accepted as a generic pronoun referring to a person of either sex, it has become common in speech and in informal writing to substitute the third-person plural pronouns they, them, their, and themselves, and the nonstandard singular themself. While this usage is accepted in casual context, it is still considered ungrammatical in formal writing."
and
 "Gender bias. . . . On the one hand, it is unacceptable to a great many reasonable readers to use the generic masculine pronoun (he in reference to no one in particular). On the other hand, it is unacceptable to a great many readers (often different readers) either to resort to non-traditional gimmicks to avoid the generic masculine (by using he/she of s/he, for example) or to use they as a kind of singular pronoun. Either way, credibility is lost with some readers."

According to The American Heritage Book of English Usage, many Americans avoid use of they to refer to a singular antecedent out of respect for a "traditional" grammatical rule, despite use of singular they by modern writers of note and mainstream publications:
"Most of the Usage Panel rejects the use of they with singular antecedents as ungrammatical, even in informal speech. Eighty-two percent find the sentence The typical student in the program takes about six years to complete their course work unacceptable. . . . panel members seem to make a distinction between singular nouns, such as the typical student and a person, and pronouns that are grammatically singular but semantically plural, such as anyone, everyone and no one. Sixty-four percent of panel members accept the sentence No one is willing to work for those wages anymore, are they?"

The Publication Manual of the American Psychological Association explicitly reject the use of singular they and gives the following example as "incorrect" usage:
 "Neither the highest scorer nor the lowest scorer in the group had any doubt about their competence."
while also specifically taking a stand that generic he is unacceptable. The APA recommends using he or she, recasting the sentence with a plural subject to allow correct use of they, or simply rewriting the sentence to avoid issues with gender or number.

Strunk & White, the authors of The Elements of Style find use of they with a singular antecedent unacceptable:
 "They. Not to be used when the antecedent is a distributive expression, such as each, each one. everybody, every one, many a man. Use the singular pronoun. [. . . ] A similar fault is the use of the plural pronoun with the antecedent anybody, anyone, somebody, someone [. . . ] The use of he as pronoun for nouns embracing both genders is a simple, practical convention rooted in the beginnings of the English language. "
Their assessment, in 1979, was
 "He has lost all suggestion of maleness in these circumstances. [. . .] It has no pejorative connotation; it is never incorrect."Joseph M. Williams, who wrote a number of books on writing with "clarity and grace", discusses the advantages and disadvantages of various solutions when faced with the problem of referring to an antecedent such as someone, everyone, no one or a noun that does not indicate gender and suggests that this will continue to be a problem for some time. He "suspect[s] that eventually we will accept the plural they as a correct singular" but states that currently "formal usage requires a singular pronoun".

According to The Little, Brown Handbook, most experts—and some teachers and employers—find use of singular they unacceptable:
 "Although some experts accept they, them, and their with singular indefinite words, most do not, and many teachers and employers regard the plural as incorrect. To be safe, work for agreement between singular indefinite words and the pronouns that refer to them [. . . ]"

It recommends using he or she or avoiding the problem by rewriting the sentence to use a plural or omit the pronoun.

The Purdue Online Writing Lab (OWL) maintains that singular they is incorrect:
 "Remember: the words everybody, anybody, anyone, each, neither, nobody, someone, a person, etc. are singular and take singular pronouns."

英国使用指南

In the first edition of A Dictionary of Modern English Usage (published in 1926) it is stated that singular they is disapproved of by grammarians and should be avoided in favour of  the generic he. Examples of its use by eminent writers are given, but it is suggested that "few good modern writers would flout [grammarians] so conspicuously as Fielding and Thackeray", whose sentences are described as having an "old-fashioned sound".

In the second edition of Fowler's, Fowler's Modern English Usage (edited by Sir Ernest Gowers and published in 1965), it is stated that  singular they is disapproved of by grammarians and, while common in colloquial speech, should preferably be avoided in favour of  the generic he in prose.  Numerous examples of its use by eminent writers are given, but it is still suggested that "few good modern writers would flout [grammarians] so conspicuously as Fielding and Thackeray".

According to the third edition of Fowler's (The New Fowler's Modern English Usage, edited by Burchfield and published in 1996)  singular they has not only been widely used by good writers for centuries, but is now generally accepted, except by some conservative grammarians, including the Fowler of 1926, who ignored the evidence:
 "Over the centuries, writers of standing have used they, their, and them with anaphoric reference to a singular noun or pronoun, and the practice has continued in the 20C. to the point that, traditional grammarians aside, such constructions are hardly noticed any more or are not widely felt to lie in a prohibited zone. Fowler (1926) disliked the practice [. . .] and gave a number of unattributed 'faulty' examples [. . . ] The evidence presented in the OED points in another direction altogether."The Complete Plain Words was originally written in 1948 by Sir Ernest Gowers, a civil servant, in an attempt by the British civil service to improve "official English". A second edition, edited by Sir Bruce Fraser, was published in 1973. It refers to they or them as the "equivalent of a singular pronoun of common sex" as  "common in speech and not unknown in serious writing " but "stigmatized by grammarians as usage grammatically indefensible. The books advice for "official writers" (civil servants) is to avoid its use and not to be tempted by its  "greater convenience", though "necessity may eventually force it into the category of accepted idiom".

A new edition of  Plain Words, revised and updated by Sir Ernest Gowers' great granddaughter, Rebecca Gowers,  was published in 2014.
It notes that singular they and them have become much more widespread since Gowers' original comments, but still finds it "safer" to treat a sentence like 'The reader may toss their book aside' as incorrect "in formal English", while rejecting even more strongly sentences like
 "There must be opportunity for the individual boy or girl to go as far as his keennness and ability will take him."The Times Style and Usage Guide (first published in 2003 by The Times of London) recommends avoiding sentences like
 "If someone loves animals, they should protect them."
by using a plural construction:
 "If people love animals, they should protect them."The Cambridge Guide to English Usage" (2004) finds singular they "unremarkable":
 "For those listening or reading, it has become unremarkable—an element of common usage.

It expresses several preferences.
"Generic/universal their provides a gender-free pronoun, avoiding the exclusive his and the clumsy his/her. It avoids gratuitous sexism and gives the statement broadest reference . . .  They, them, their are now freely used in agreement with singular indefinite pronouns and determiners, those with universal implications such as any(one), every(one), no(one), as well as each and some(one), whose reference is often more individual . . ."The Economist Style Guide refers to the use of they in sentences like
 "We can't afford to squander anyone's talents, whatever colour their skin is."
as "scrambled syntax that people adopt because they cannot bring themselves to use a singular pronoun".The New Hart's Rules is aimed at those engaged in copy editing, and the emphasis is on the formal elements of presentation including punctuation and typeface, rather than on linguistic style but—like The Chicago Manual of Style—makes occasional forays into matters of usage.
It advises against use of the purportedly gender-neutral he, and suggests cautious use of they where he or she presents problems.
 ". . . it is now regarded. . . as old-fashioned or sexist to use he in reference to a person of unspecified sex, as in every child needs to know that he is loved. The alternative he or she is often preferred, and in formal contexts probably the best solution, but can become tiresome or long-winded when used frequently. Use of they in this sense (everyone needs to feel that they matter) is becoming generally accepted both in speech and in writing, especially where it occurs after an indefinite pronoun such as everyone or someone, but should not be imposed by an editor if an author has used he or she consistently."

The 2011 edition of the New International Version Bible uses singular they instead of the traditional he when translating pronouns that apply to both genders in the original Greek or Hebrew. This decision was based on research by a commission that studied modern English usage and determined that singular they (them/their) was by far the most common way that English-language speakers and writers today refer back to singular antecedents such as whoever, anyone, somebody, a person, no one, and the like."

澳大利亚使用指南

The Australian Federation Press Style Guide for use in preparation of book manuscripts recommends "Gender-neutral language should be used", stating that use of they and their as singular pronouns is acceptable.

英语语法使用指南

According to A Comprehensive Grammar of the English Language (1985):
 "The pronoun they is commonly used as a 3rd person singular pronoun that is neutral between masculine and feminine. . . . At one time restricted to informal usage. it is now increasingly accepted in formal usage, especially in [American English].The Cambridge Grammar of the English Language discusses the prescriptivist argument that they is a plural pronoun and that the use of they with a singular "antecedent" therefore violates the rule of agreement between antecedent and pronoun, but takes the view that they, though primarily plural, can also be singular in a secondary extended sense, comparable to the purportedly extended sense of he to include female gender.

Use of singular they is stated to be "particularly common", even "stylistically neutral" with antecedents such as everyone, someone, and no one, but more restricted when referring to common nouns as antecedents, as in
 "The patient should be told at the outset how much they will be required to pay."
 "A friend of mine has asked me to go over and help them . . ."

Use of the pronoun themself is described as being "rare" and "acceptable only to a minority of speakers", while use of the morphologically plural themselves is considered problematic when referring to someone rather that everyone (since only the latter implies a plural set).

There are also issues of grammatical acceptability when reflexive pronouns refer to singular noun phrases  joined by or, the following all being problematic:
 "Either the husband or the wife has perjured himself." [ungrammatical]
 "Either the husband or the wife has perjured themselves." [of questionable grammaticality]
 "Either the husband or the wife has perjured themself." [typically used by only some speakers of Standard English].

On the motivation for using singular they, A Student's Introduction to English Grammar''' states
 "this avoidance of he can't be dismissed just as a matter of political correctness. The real problem with using he is that it unquestionably colours the interpretation, sometimes inappropriately. . . he doesn't have a genuinely sex-neutral sense".

The alternative he or she can be "far too cumbersome", as in
 "Everyone agreed that he or she would bring his or her lunch with him or her.
or even " flatly ungrammatical", as in
 "Everyone's here, isn't he or she?

"Among younger speakers", use of singular they even with definite noun-phrase antecedents finds increasing acceptance, "sidestepping any presumption about the sex of the person referred to", as in
 "You should ask your partner what they  think."
 "The person I was with said they hated the film." Example given by Huddleston et al.

语法和逻辑分析

Steven Pinker suggests that "singular" they and plural they can be regarded as a pair of homonyms — two words with different meanings but the same spelling and sound.  However, this analysis is not extended to you, another originally plural pronoun that has come to have singular use.

分布

Distributive constructions apply a single idea to multiple members of a group.
They are typically marked in English by words like each, every and any. The simplest examples are applied to groups of two, and use words like either and or—"Would you like tea or coffee?". Since distributive constructions apply an idea relevant to each individual in the group, rather than to the group as a whole, they are most often conceived of as singular, and a singular pronoun is used.
 "England expects that every man will do his duty."—Nelson (1806, referring to a fleet crewed by male sailors)
 "Every dog hath his day." —John Ray  A Collection of English Proverbs (1670), originally from Plutarch, Moralia, c. 95 AD, regarding the death of Euripides.
However, many languages, including English, show ambivalence in this regard. Because distribution also requires a group with more than one member, plural forms are sometimes used.

引用和非引用照应语

According to the traditional analysis, English personal pronouns (e.g. his, her, their) are typically used to refer backward (or forward) within a sentence to a noun phrase (which may be a simple noun). This reference is called an anaphoric reference, and the referring pronoun is termed an anaphor.

The so-called singular they is morphologically plural, and is accompanied by a plural verb. However, it is often used in circumstances where an indeterminate antecedent is signified by an indefinite singular antecedent; for example,
 "The person you mentioned, are they coming?"
In some sentences, typically those including words like every or any, the morphologically singular antecedent does not refer to a single entity but is "anaphorically linked" to the associated pronoun to indicate a set of pairwise relationships, as in the sentence:
 "Everyone returned to their seats." (where each person is associated with one seat)

One explanation given for the use of they to refer to a singular antecedent is notional agreement, when the antecedent is seen as semantically plural, as in the Shaw quotation
 "No man goes to battle to be killed." . . . "But they do get killed. [Merriam-Webster's Concise Dictionary of English Usage]
In other words, in the Shaw quotation no man is syntactically singular, demonstrated by taking the singular form goes; however, it is semantically plural (all go [to kill] not to be killed), hence idiomatically requiring they.

Linguists like Pinker and Huddleston explain sentences like this (and others) in terms of bound variables, a term borrowed from logic. Pinker prefers the terms quantifier and bound variable to antecedent and  pronoun.

The word reference is traditionally used in two different senses:
 the relationship between an anaphor (e.g. a pronoun) and its antecedent;
 the relationship between a noun phrase and the real-world entity (the referen).

With a morphologically singular antecedent, there are a number of possibilities, including the following:
 coreferential, with a definite antecedent (the antecedent and the anaphoric pronoun both refer to the same real-world entity):
 "Your wife phoned but she didn't leave a message."
 coreferential with an indefinite antecedent:
 "One of your girlfriends phoned, but she didn't leave a message."
 "One of your boyfriends phoned, but he didn't leave a message.
 "One of your friends phoned, but they didn't leave a message."
 reference to a hypothetical, indefinite entity
 "If you had an unemployed daughter, what would you think if she wanted to accept work as a pole dancer?"
 "If you had an unemployed child, what would you think if they wanted to accept work as a mercenary or a pole dancer?"
 a bound variable pronoun is anaphorically linked to a quantifier (no single real-world or hypothetical entity is referenced):
 "Nobody knew where they were."
 "Every woman present sat with their breasts in full view."

认知效率

复数代词they用于指代单数先行词的用法逐渐增多，一些研究尝试断定这种用法会不会让理解变得更“困难”。
此研究之一是，《性别中性搜寻：单数they是对性别通用he在认识上的一个高效替代吗？》Foertsch与Gernsbacher著，他们发现“单数they是对性别通用he或she在认识上的一个高效替代，尤其是当先行词没有明确所指的时候”（例如anybody或者a nurse），而很少用于指代确定的一个人的时候（例如a runner I knew或者my nurse）。单数they的语句读起来“就像包含了先行词具有常规性别映像对应的有性代词的语句一样快”（例如护士用she，卡车司机用he），并且“比包含了与先行词常规性别映像的性别相反有性代词语句更快”（例如护士用he，卡车司机用she）。

与其它代词的对比

代词they的单数用法和复数用法可以与代词you作比较。曾经you只能作为复数使用，对应的单数形式为thou。但是在大约1700年左右，you取代了thou，作为单数形式使用，并且动词依然使用复数形式。

另见
 一致性
 
 
 
 
 性別酷兒

注

参考资料

原例子的源头

 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
quoted in Reader' Digest, 1983, as an example of its awkwardness when referring to both sexes.

参考书目
 

 

 

 

 
 
 
 
 

 
 
 
 .N.B.: This is not the English usage authority Henry Watson Fowler.

外部链接
 "Anyone who had a heart (would know their own language) ", Geoff Pullum著, 电台访谈的摘录

英語語法
非二元性別
語言中的性別
语法数