Why is it not "Both of Yous", when we use "Both of You"? [duplicate]

Solution 1:

You and ye used to be the plural forms of the second person pronoun. You was the accusative form, and ye was the nominative form.

Because of this, you still conjugates verbs in the plural form even when it is singular; that is, you are is correct even if you is only referring to one person.

Thee and thou used to be the singular forms. Thou was the nominative form, and thee was the accusative form. Thy and thine were the genetive forms, and their use followed the same rules as a and an.

Solution 2:

You is the plural.

Thou is the singular form of you.

Thou has now disappeared from common use and is used only to address God.

The process resulting in the use of the singular pronoun to express intimacy and the plural pronoun to mark respect or social distance is termed T-V_distinction, after the Latin tu and vos and is found is many languages, especially of the Proto Indo European family tree.

See for instance, in addition to the Latin form above:

• French: tu => vous
• German: du => ihr (2nd person plural) or Sie (3rd person plural)
• Mandarin 你 (nǐ, you informal) => 您 (nín, you respectful) compared to (nǐmen, 你们, you to several persons).

Even some languages that seem not to comply exactly (because they don't seem to use the 2nd-person plural) actually hide a form a compliance.

• Spanish: tu => vos (obsolete, 2nd-person plural archaic form).
• Italian used to use voi (2nd person plural).
• The você of Portuguese is a contraction of vossa mercê (your mercy) which is an implicit 2nd person plural.

All in all, English has pushed T-V distinction so far that thou is not used anymore in common speak.