Generic antecedent

Generic antecedents are representatives of classes, referred to in ordinary language by another word, in a situation in which gender is typically unknown or irrelevant. These mostly arise in generalizations and are particularly common in abstract, theoretical or strategic discourse. Examples include "readers of Wikipedia appreciate their encyclopedia", "the customer who spends in this market".
The question of appropriate style for using pronouns to refer to such generic antecedents in the English language became politicized in the 1970s, and remains a matter of substantial dispute.

Treatment in various languages

Many languages share the following issue with English: the generic antecedent is a representative individual of a class, whose gender is unknown or irrelevant, but pronouns are gender-specific. In languages such as English that distinguish natural gender in pronouns but not grammatical gender in nouns, normally masculine, but sometimes feminine, forms of pronouns are used for the generic reference, in what is called the generic usage of the pronoun. The context makes the generic intent of the usage clear in communication.

Example: An ambitious academic will publish as soon as she can.

Unless there is reason to believe the speaker thinks ambitious academics are always female in the relevant context, the use of she in this sentence must be interpreted as a generic use. Traditionally both he and they were used for this purpose but, particularly since the nineteenth century, English style guides have frequently recommended the otherwise masculine he as a singular generic pronoun. Since the middle of the twentieth century the use of he for this purpose has been discouraged, partly because use of he is perceived as subtly biasing the listener to assume the antecedent is masculine. Various alternatives have been proposed, including the ubiquitous but controversial singular they.

French

In French both the singular and plural pronouns in the third person are marked for grammatical gender, and the antecedent always has grammatical gender. The masculine form of "they", ils, is always used when referring to a plural and grammatically masculine antecedent, while for plural antecedents that are grammatically feminine the feminine form elles of "they" is used. Likewise, in the singular the third person pronoun il is used to refer to grammatically masculine antecedents and elle is used to refer to grammatically feminine antecedents. Thus, for both generic and non-generic antecedents, the natural gender of the antecedent, whether known or unknown, is irrelevant, as the deciding factor for the choice of a referring pronoun is the grammatical gender of the antecedent.
Some French speakers advocate the use of created gender-free pronouns, such as illes or els for ils et elles and they and celleux or ceulles for celles et ceux and those.

Mandarin Chinese

In spoken Mandarin Chinese, and in the pinyin form of writing Mandarin in the Latin alphabet, there is no distinction between "he" and "she", nor is there a distinction between "they " and "they ". However, when Mandarin is written in characters, a gender distinction is made: tā is written as 他 or 她 for "he" or "she" respectively, with -men added for the plural. For a plural generic antecedent such as "people ", the referring pronoun will always be written as the masculine plural form unless the generic group is known to be inherently female, in which case the feminine form is used. For a singular generic antecedent such as "someone", the referring pronoun is always written as the masculine singular form unless the generic antecedent is known to be inherently female.

Gender in English pronouns

If an antecedent is a thing, either specific or generic, rather than a person, the appropriate pronoun to refer back to it is it, and no difficulty arises. Likewise, if the antecedent is more than one thing, again either specific or generic, the pronoun they is used to refer back to it, and again no difficulty arises.
When the antecedent is a specific person, the correct referring pronoun is either he or she, depending on the person's gender. When the antecedent is a specific group of two or more people, the pronoun they is used, again without any difficulty arising. And when the antecedent is generic and plural, again the pronoun they is used and is not problematic, because they is not gender-specific.
But difficulty arises in choosing a singular pronoun to refer to a single, unspecified human. In particular, the overlap of generic use with gender role stereotyping has led to controversy in English.

A nurse should ensure that she gets adequate rest.
A police officer should maintain his fitness.
A dancer should watch her diet carefully.
A boss should treat his staff well.

In these examples, some speakers might mean that all nurses are female, or that all bosses are male, while others might intend the pronouns as generic and hence gender-unspecific. Ambiguity arises from the possibility that the listener might interpret the meaning differently from what the speaker intended.

Approaches taken in English

Speakers of all languages use words both to make distinctions and to generalize:

Example of distinction: My mother thinks..., but my father says....
Example of generalization: Parents believe....
Example of generalization: Any parent believes....

What has become controversial among users of English is the choice of pronoun to refer back to a generalized, and hence generic, singular antecedent such as any parent, or every parent. Examples of accepted, disputed, and impossible constructions in English include:

25px All people get hungry, so they eat. Acceptable
25px All people get hungry, so she eats. Incorrect if all people is the intended antecedent of she
25px Each one gets thirsty, so he drinks. Disputed
25px Each one gets thirsty, so they drink. Acceptable Long in use ; condemned by some older sources, such as The Elements of Style, but endorsed by many modern style guides.
25px Each one gets thirsty, so he or she drinks. Awkward and recommended against by the Chicago Manual of Style, et al.
25px When a person is tired, she sleeps. Disputed

English guidelines before the 1980s supported the use of he as a singular pronoun that can refer to both men and women. Use of the generic he, however, has been decreasing since the 1960s.
Many recent style guides discourage generic constructions or accept approaches other than the generic he. Some writers prefer to alternate between male and female generic usage to provide clarity without the appearance of bias. Other speakers intentionally use female generic forms as a political or cultural statement against the conventional practice of generic use of the masculine form. A study of English language usage over the past twenty years shows that they is now the most common way that modern speakers and writers refer back to generic antecedents.

Modern solutions

Speakers opposed to gender role stereotyping often use one of the following strategies.

A boss should treat her staff well. Bosses should treat their staff well.
A boss should treat their staff well..
A boss should treat eir staff well.

There is historical precedent for the third option as well as popular contemporary usage. However, there are contemporary, as well as historical, style guides that discourage this option. In 2000, the Usage Panel of The American Heritage Dictionary wrote:
By their 2022 update, the dictionary reported "their resistance has declined over time":

Other alternatives

Options other than generic pronouns, rephrasing in the plural, or using they can be well suited to some contexts, but problematic in others.

A boss should treat her or his staff well.
If he does, it is good. Thon will be happy and so will they.

The indefinite personal pronoun, one, is suitably singular and unspecific with respect to gender; but it can take only "one" as an antecedent.One takes care of one's own.

Opinions

Some modern prescriptivists argue from the valid use of they in certain contexts, to making it valid or even mandatory in all. Other prescriptivists argue that generic he should be proscribed. Both these points of view have found many followers; however, they generally do not accurately describe the usage or rationale of the wide range of options common in the English language.