Adult Sheldon: It was past my bedtime, but who could sleep with a page-turner like Meditations on First Philosophy by René Descartes? Descartes was more than just a philosopher. He was also the mathematician who invented the Cartesian plane. If you've ever enjoyed that X squared plus Y squared equals K is a circle, you can say merci beaucoup to Monsieur Descartes.

Adult Sheldon: I didn't realize until years later that my father was only asking questions about lightning and thunder to cheer me up. In fact, he would often pretend to be dumb just to make me feel better.

Adult Sheldon: My father didn't always get the credit he deserved. The advice he gave me actually worked out pretty well. Of course, I never told him.
George Sr.: Talked to Billy.
Missy: Why would you do that?
George Sr.: No, it was good.
Missy: Stay out of my life.
Adult Sheldon: He may not have been the world's greatest dad. But maybe we weren't the world's greatest kids.

Adult Sheldon: Visiting Tam's house for the first time was an emotional roller coaster.
For example, it's traditional in Vietnamese homes to have gruesome religious iconography near the entrance. I did not like that.
However, it's also customary to not wear shoes around the house for sanitary reasons. I did like that.
Interestingly, one of the main ingredients in Vietnamese cooking is an extremely pungent condiment known as fish sauce. I did not like that.
But before every meal, it's common for everyone to wash their hands and face. I did like that.
Forks are not customary in a Vietnamese household. I did not like that.
And instead of napkins, there was one towel for everyone to share at the table. Seriously, what are they thinking?

Professor Ericson: So we learned that the theory of knowledge poses some very serious problems.
Sheldon: [enters] Excuse me, Professor Ericson. I've done a little reading since last we spoke, and I'm prepared to show you that everything we know about science is true.
Professor Ericson: Well, I am all ears.
Sheldon: You said I couldn't truly know anything, but there is one thing that I do know. If I question, I must think; If I think, I must exist. Cogito, ergo sum: I think, therefore I am.
Professor Ericson: You're right.
Sheldon: You're darn right I'm right.
Professor Ericson: Guys, g-give it up for Sheldon. [applause] Now for a job well done... here is a flower full of sweet nectar.
Sheldon: Why would I want that?
Professor Ericson: Because you're a butterfly and this is just your dream.
Sheldon: I'm not a butterfly.
Professor Ericson: Are you sure? [laughs]
[Sheldon wakes up:]
Sheldon: It was a dream. Oh, no. [camera pans out] Help! I'm a butterfly! Nothing I know is real! Everything is a dream! Missy, help! [Missy holds a fly swatter] No!
[Sheldon wakes up:]
Sheldon: Missy, am I awake or is this a dream?
Missy: Shut up, dingus.
Sheldon: Okay, I'm awake.

Sheldon: I stopped at the library today and picked up books on epistemology, Descartes's dream argument and the foundations of scientific logic. Do you know what she's going to do?
Meemaw: Rue the day?
Sheldon: The day, the night. If it's rue-able, she's going to rue it.

Mary: Hey, Brenda.
Brenda Sparks: She didn't want you to walk her in?
Mary: No. How about Billy?
Brenda Sparks: Oh, I walked him in. Found his homeroom. Explained that "homeroom" is different than his room at home. Still not sure he gets it.
Mary: Tough day.
Brenda Sparks: Yeah.
Mary: You want to get some coffee?
Brenda Sparks: I was thinking vodka, but coffee will do.