This is really the theme to end all themes. What's interesting here is that Wicked isn't all that abstract. These often esoteric themes recur in two very concrete thematic questions in Wicked: What is a soul, and what exactly is an Animal? Elphaba seeks an answer to both of these questions but, ironically, she denies the existence of her own soul. She constantly ponders the big questions about life, but she never finds a definite answer. (Though those ruby slippers might come close.)
Questions About Life, Consciousness, Existence
Why does Elphaba deny that she has a soul, and why does she want one at the end of the novel? What exactly is a soul in her opinion?
How do the debates surrounding Animals play a thematic role in the book?
Elphaba and Fiyero debate the existence of a human conscience (3.9), Elphaba arguing that it's really just instinct. What does she mean by this, and how is this debate significant to the novel as a whole?
Fiyero accuses Elphaba of valuing certain "realer" people over others (3.8-9). Who and what does Elphaba define as more "valuable," and what does this tell us about her view of life and as a character.