One other critical theme is the element of self discovery through voyage. Homer must experience the world in the attempt to find himself. Leaving the protected and caring world of Dr. Larch and the orphanage allowed Homer to understand much about emotional experiences and the notion of personal growth and development. The theme here is that the journey allows individuals the chance to grow and understand both the world and themselves in different ways than they did prior to the voyage. In the process, the return home creates a unique sensation in the individual where they have to balance the life and person they were before and after the journey.
One of the main themes in The Cider House Rules novel by John Irving is that of the obligations owed to society by individuals. For example, the doctor in the story (an obstetric doctor) can decide to aid a birth or facilitate an abortion in a way he feels allows him to decide what is best in any one set of circumstancees.
Another strong theme is that of the family in society. Neither of the "families" present in the novel are conventional, one is a school or place of work (an artificial family setting) and the other a "trinity" of three. These "families" represent the way in which our society is changing and moving away from the conventions that bordered it in the past.
There are many themes. I will unpack what I think is the major theme.
There is the theme of abortion. However, this theme is argued from both sides, which makes the movie nuanced and a good one. On the one hand, the movie portrays abortion from a positive angle by portraying what happens when it is outlawed. In short, women resort to illegal ones that are dangerous. Also it also explore a possible area where abortion might be considered acceptable by many people - incest.
On the other hand, this movie is also about orphans who were not aborted. They have a right to live and enjoy life. In the end, there is no one answer.