Humanity
The key question posed in the book is that of humanity, and chiefly, what it is that makes a person human. Carey is a droid, and her intelligence is definitely artificial. AI generally does not come with a range of emotions attached to it; any emotional expression has been pre-programmed by the person who made the droid in the first place. Yet, we see Carey starting to feel affection, even love, and to bond with her human employers and family. This throws up the question of whether it is biology, or emotion, that makes a person human.
Artificial Intelligence
Although the novel is technically in the science fiction genre, artificial intelligence exists in the present, although the ethical use of it is still a matter of debate. The novel;s theme of AI is mostly a narrative theme; what happens to Carey in the course of her "life" is the novel's plot, and there is really little ethical debate about her one way or another. However, the larger theme of our use of AI, its potential and the potential for abuse is one of the key themes of the book.
Memory
Carey and Mildred are really in the same boat; neither can draw on their own, original memories, and both need the help of others to re-create memory for them. Any memories that Carey has have been implanted by the person who created her, and have no real emotional attachment to them. Mildred has enormous emotional attachment to her memories, but is frustrated because although she knows there is something that she is attached to, she cannot remember what it actually is. The theme of memory pertains entirely to the loss of memory, and to the connection that we have to the emotions of it, even when we do not know what the memories actually are.
