What is the theme in One Flew Over the Cuckoo's Nest by Ken Kesey?

There are many themes in this story. Control is one of them. Both Nurse Ratched and McMurphy seek control over the ward. They want to instil their own sense of purpose for these men. Mental illness is also a theme. In many ways Nurse Ratched and the hospital enable these men to stay mentally ill. McMurphy challenges this ethos.