LitCharts assigns a color and icon to each theme in The Sirens of Titan, which you can use to track the themes throughout the work.
Free Will vs. External Control
Religion and the Search for Meaning
Wealth, Power, and Inequality
Human Intelligence, Foolishness, and Hubris
Summary
Analysis
Mercury sings “like a crystal goblet,” with half of the planet stuck in an eternal day and the other in eternal night. There are creatures who live in Mercury’s caves and who are nourished by the planet’s singing. These aliens reproduce via “flaking.” They don’t have sex differentiation, or any real childhood stage. They cannot cause each other harm, and they only have one sense: touch. Their communication is limited to two phrases—“Here I am,” and “So glad you are.” They exist in beautiful patterns on the phosphorescent walls of the cave, and on Earth they are called “harmoniums.”
At this point the novel takes a decidedly surreal, almost abstract turn. The description of Mercury’s strange, beautiful natural landscape is a stark contrast to the pointless horrors of the war between Earth and Mars.
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Themes
When Unk and Boaz approach Mercury, it almost looks like a densely populated, civilized planet. However, this is just an illusion. Unk cries, thinking about Bee, Chrono, and Stony. He thinks about the name “Malachi Constant” but doesn’t know what it means. Unk and Boaz’s automatically-driven ship has trouble landing on the planet’s surface, and they descend into “inky blackness.” The ship keeps descending in “lurches,” until eventually the two passengers can see a yellow light coming through the window. The ship has successfully landed inside one of Mercury’s caves.
Again, the surreal nature of this passage almost conjures a kind of dream sequence. While everything that happens to Unk and Boaz is real, they are so far from human civilization that it seems like it isn’t. In attempting to exert free will and desert the Martian Army, it seems as though Unk and Boaz have underestimated the potential dangers and bizarre experiences that could be in store for them on Mercury.
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Themes
Astonished by the sights outside, Boaz exclaims that they have landed “right in the middle of a Hollywood night club.” However, despite how pleasant the landscape outside seems, it is actually a “vacuum,” and when they open the door it immediately causes their lungs to start bleeding. They shut the door immediately. However, after loading themselves with goofballs and holding their ears and noses, they venture out, exploring the area where the ship has landed. They notice the harmoniums, but find them “ghastly.” They remain in a state of disbelief about their situation; Boaz suggests they go out of the cave and attempt to communicate with the people living in the (illusion of) skyscrapers above.
The fact that Boaz and Unk have descended into a cave and are now experiencing delusions about their situation, falsely believing there is a civilization above, links this passage to Plato’s Cave, a famous philosophical parable. The story distinguishes between those who believe in the delusions of the material world versus those who seek to know the truth of reality via philosophy—a distinction with a clear connection to the novel, and particularly to Unk’s experience in the army.
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Themes
However, while the ship was able to descend into the cave on autopilot, going back up is not as easy. Trying to move, the ship emits a screaming sound, and it becomes clear that it is wedged inside the cave. Each time the ship moves a little, it overheats and shuts down, and falls back onto the cave floor. Boaz exclaims that it’s hopeless. However, at this moment Unk looks out the window and notices the harmoniums are spelling out letters to make a message. The message reads, “IT’S AN INTELLIGENCE TEST!”
Again, the message being spelled in harmoniums (as well as the very existence of the harmoniums themselves) gives this part of the novel a dreamy, surreal quality. Yet the message indicates that Unk and Boaz have not been released from the clutches of Rumfoord’s elaborate scheme just yet.