It is generally accepted that Shi evolved from a pronoun to a assertive copular and to a focus marker.

“是”从代词演变为断定系词，进而成为焦点标记，是语法界普遍接受的事实。

youdao

It is generally accepted that Shi evolved from a pronoun to a assertive copular and to a focus marker.

“是”从代词演变为断定系词，进而成为焦点标记，是语法界普遍接受的事实。

youdao