How did you become singular?

The history of the pronoun you provides a good example of the effect social forces can have on the language. Originally, the pair ye and you was used along with thee and thou to refer to people in the second person, ye and you for plural and thee and thou for singular. You began as the grammatical object, used in the following ways:

I see you sitting there together.

I gave you six apples, three for each.

These uses are known respectively as the accusative and dative cases. The singular for this use would be thee:

For thee there are three apples.

Of thee I sing.

When the second person plural was used as a grammatical subject, ye was used.

Seek and ye shall find.

This use is called the nominative case. The singular for this use would be thou:

How great thou art.

As far back as the 14th century, the plural forms ye and you began to be used to address one person—usually a superior—as a mark of deference and respect. This change could have been influenced by the first-person plural we (the royal “we”) used by sovereigns or reflected the impact of French politeness at work in Middle English. Once this usage of the polite plural began, it gradually grew. This is where social forces came into play: once people begin such a use, it must grow, since people would rather be polite than risk offending others in cases of doubt. As the use of the plural increased, the singular use decreased accordingly: by the beginning of the 17th century, thou and thee marked only an intimate or personal relationship or a superior-to-inferior relationship. It was even sometimes used to show deliberate disrespect. Queen Elizabeth I seems to have used only you in writing, and a user of her prestige must have given you a boost.

By about the middle of the 16th century the contrast in function between ye and you began breaking down, with the effect that you was more frequently used as a subject pronoun as use of ye decreased.

The loss of thee and thou—a singular pronoun for everyday use—was clearly noticed by English speakers.

Initially, the distinction between singular you and plural you was signaled by verb agreement; you was for the singular continued in polite if informal use well into the 18th century before it lost respectability. Special plural forms were later contrived to hold you chiefly to singular use, such as you-all , you-uns, yez, and youse. None of them became standard.

So the simple social drive of good manners has in a few centuries completely remade the second person pronoun in English. No doubt the social pressures of today will work changes in the language as well. The chances are, however, that most changes they bring about will not be rapid.