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.

Principal Petersen: Our next young speaker needs no introduction, but that didn't stop him from writing one and making me read it. [laughter] "Fun fact." [audience groans, murmurs] I hear you. "The word 'valedictorian' is from the Latin 'valedicere,' meaning 'to say farewell.' It is primarily used in the United States, Canada, the Philippines and Armenia." Maybe that fact's more fun in Armenia. Please welcome your valedictorian, Sheldon Cooper.
Mary: Yay, Shelly!
Sheldon: Hello. I'm not very comfortable speaking in front of crowds. But there's a technique to reduce stage fright by focusing on one person in the audience and delivering your speech just to them. That's what I'll be doing today. If it weren't for this person, I wouldn't be here right now. They've taught me a lot, and it's by their example that I found the courage to move forward into this new and exciting chapter of my life. Missy... ...this is for you. Change can be scary, but I know we're going to be fine... ...because like you said, "It's okay to be scared. We just have to do it anyway." So if any of my fellow graduates are nervous about the future, know that you're not alone. I suggest you all try to be as brave as my twin sister. That's my plan. Missy, I wish I could give you advice about middle school, but I was so smart, I skipped it. If you make it to high school, we'll talk. Thank you. [applause]

Mary: Too bad. We are going.
Sheldon: Class is starting tomorrow. I'm not going anywhere.
Mary: Sheldon, do not argue with me. You are going home.
Sheldon: Mom, the people of Germany are obsessed with rules and devoid of humor. I am home.

Mary: You understand that some people are going to be intimidated by you, because of how smart you are?
Sheldon: Or maybe they'll recognize my intellect and make me their leader.

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.

Pastor Jeff: Dear Heavenly Father, as we return to school, we look to your eternal...
Billy Sparks: [stands] I pledge allegiance to the...
Pastor Jeff: Billy, it's not the pledge.

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.