Modern critics divide the book of Isaiah into three sections: (1) chapters 1-39, (2) chapters 40-55, and (3) chapters 56-66.
The claim is made that the latter two sections, which contain very specific prophecies concerning events that took place hundreds of years
after Isaiah died, were actually written by disciples of Isaiah living during
those later periods of Judah’s history and carrying on his mission under
his name.
Naturally, conservative scholars disagree.