LitCharts assigns a color and icon to each theme in Simon vs. the Homo Sapiens Agenda, which you can use to track the themes throughout the work.
Agency and Control
Identity and Assumptions
Relationships and Empathy
Family, Change, and Growing Up
Summary
Analysis
The Saturday after Christmas, Simon, Alice, and Nora go to Waffle House for breakfast. Alice smiles at a guy across the room that Simon thinks looks vaguely familiar. Alice says the guy is Carter Addison and starts to suggest that Simon talk to him, but Simon cuts her off and leaves the restaurant. Nora joins him in the car after a few minutes, and Simon tells her that Martin, Carter Addison's brother, is the one who posted on creeksecrets. He briefly explains that Martin likes Abby and thinks that Abby has a crush on Simon. Alice comes out of the restaurant and angrily demands that Simon let her drive home. She wants to know why he left the restaurant. Nora tells Alice to let it go, which is something she never does.
When Simon mentions that this is the first time that Nora has ever stood up to Alice, it shows how the family dynamics are beginning to change. This change continues when Simon chooses to confide in Nora, something that also seems like a new turn in their relationship. Though Alice means well by suggesting that Simon talk to Martin's brother, Simon interprets it as an assumption that they should get on just fine only because they're both gay in small-town Georgia.
Active
Themes
On New Year's Eve, Simon and Mom argue about Simon needing to clean the basement before having a party. She also says that they'll need to talk about how to handle Nick sleeping over in the future, which makes Simon angry. Regardless, the party proceeds as Nick, Leah, Abby, and Simon's parties usually do. Nick pulls out a guitar and in a lull, Leah mentions that "they" took the post down. She insists they don't have to talk about it but asks if Simon knows who wrote it. He admits he does, but won't say who.
Despite the fact that Simon describes the party as mostly normal, it's clear that things are different this year—remember that Abby is a new arrival in the friend group, and Leah's mention of the creeksecrets posts suggests that they're going to have to make room for Simon's changing identity.
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Themes
Finally, Simon says that he is gay, but he doesn't want it to be a big deal. Nick simply says "okay," which Abby finds an inadequate response. She suggests that Nick say something supportive or hold Simon's hand like she did. Leah is upset to learn that Simon already came out to Abby, and Simon rushes to get everyone ice cream. After midnight, when Nick and Abby are already asleep, Simon asks Leah if she's mad that he told Abby first. Leah insists she has no right to be mad, but Simon can tell she's upset. He refuses to tell her how his sexuality ended up the subject of a Tumblr post and pretends to fall asleep.
Nick's response appears to be exactly what Simon wants, which does give some credence to Simon's earlier assertions that he and Nick know each other well enough they don't have to talk about much. Though Simon is certainly not required to share everything with Leah, it's worth noting that his unwillingness to include her in what he knows is definitely making her feel like she's less important to him.