The tripartite structure of A Clockwork Orange is there to give shape to Alex's moral development. By dividing his life into three discrete parts, Burgess shows us Alex's transition from a kind of moral childhood with its total lack of control and responsibility toward a more adult understanding of the world, albeit a highly imperfect one.

It's notable that each part of the book consists of seven chapters, which means that there are twenty-one chapters in total. This is a highly symbolic number, as twenty-one is traditionally regarded as the age of adulthood.

Even so, Alex, like most adults, is nonetheless vulnerable to moral backsliding. In the third part of the novel, Alex the Good briefly reverts back to Alex the Bad, the ultraviolent droog of the first part. Nonetheless, Alex is able to move on, finding a wife and settling down for what could well turn out to be a life of wedded bliss.

Though Alex remains, in many respects, a deeply troubled young man, one can still observe a dramatic difference in his character. Real moral growth can clearly be identified, even if the methods used to put him on the straight and narrow—such as Ludovico's Technique—are ethically problematic, to say the least. At any rate, by the time we've reached the twenty-first and final chapter, there's little doubt that Alex has matured. How long that will last, though, is anyone's guess.