The Sirens of Titan explores the illusion of free will. Throughout the novel, humans are forced to reckon with their own lack of control over their destinies. Despite their wealth and privilege, for example, Constant and Beatrice can do nothing to prevent Rumfoord’s predictions from coming true. They do everything in their power to assert their free will, with Constant essentially bankrupting himself and Beatrice trying to avoid Rumfoord’s presence. They fail, nonetheless. Constant’s desire to assert his free will is especially ironic given the way in which his father made his fortune: Noel Constant invested in certain stocks depending on whether their initials correlated with words in the Bible, thereby giving himself up to fate and profiting hugely from doing so. In an attempt to defy this kind of divine fortune and abandonment of free will, Constant achieves the opposite. As such, the opening sections of the novel suggest that the characters who accept that they have no free will are richly rewarded, while those who are desperate to demonstrate their own agency are ruined in the process.

Rumfoord is not especially pleased that he has the power of prophecy. He knows how and when things will occur, though he does not necessarily know why.