Liberal scholars continue to put forth the "evidences" for multiple authors over multiple generations for the book of Isaiah.
Webb makes several criticisms of such an idea. One of the best that struck me: "Equally difficult for the majority view is the need to maintain that the author of chapters 40-55 should have had his name either completely forgotten or deliberately suppressed...In every other instance of prophetic commissioning in the Old Testament, the prophet is either addressed by name or clearly identified in the framing narrative, and the names of those so called are revered and honoured. Even where there is a close 'master-disciple' relationship between two prophets, as with Elijah and Elisha, each is remembered by name. but in the case of 'Second Isaiah', we are required to believe that a disciple who receives a separate commissioning almost a century and a half after the death of his master, and whose own ministry rivals or even surpasses that of his mentor, has had his identity completely suppressed!" - Webb, p36.