Not every economist is happy with the neo-classical theory of wage determination. For example, Moshe Adler, in "Economics for the Rest of Us", gives...

Not every economist is happy with the neo-classical theory of wage determination. For example, Moshe Adler, in “Economics for the Rest of Us”, gives us quite a scathing critique of that theory. One of his issues is that it is impossible to calculate the VMP of individual workers. Explain that argument, both logically and using the evidence Adler provides.