P and Q

This past week, during a time in the afternoon which is certainly considered "The Crunch" to most New York City professionals, I sent a frantic AOL Instant Message to an IP attorney friend who works in in a huge corporate office in Times Square:

Me: "Help! Do you know what "P" and "Q" stand for?"
Him: "What?"
Me: "You know, P and Q. We're in the middle of a logic lesson. You took logic or philosophy, right?"
Him: "Um..."
Me: "Hello?"
Him: "You mean like in math, right?"
Me: "Yes, right. It's used in Calculus. But right now I just need to know what P and Q mean."
Him: "Did we discuss this before?"
Me: [totally embarassed now] "Erm, no...?"

How did this happen? Exercise Four in Introductory Logic by Douglas J. Wilson and James B. Nance. Alexander understood consistency, implication, logical equivalence, and independence. But what do the funny "P" and "Q" stand for? Why are those letters chosen? Why not A and B? Why? Why? Why? Half-an-hour with Google did not help me.

[Me, now dazed in my chair, suffering a flashback to college. Professor Xerohemona, a wonderful Greek woman whose Ph.D. was in Philosophy, is now speaking]

Professor Xerohemona: "If P is true, then Q must also be true"
Unruly college student: "Professor, what do "P" and "Q" mean? You talk about stuff without explaining it. Dude! You suck!"
Professor Xerohemona: "Unruly student, please wait for me outside."
Unruly college student: "Are you for real? Dude, are you on your period?"
Professor Xerohemona: "άέήγθζεβλχπσψΕΘΓΠΩΣΥΕΕΘΓΠΩΣΥΕΕ!!!!!WAIT OUTSIDE!!!"

And of course, until I can come up with a Really Good Answer as to why it's P and Q, the lessons themselves will face the inevitable scrutiny of my 6th grade thinker.

And now, a funny that I borrowed (thank you, Poppins Classical Academy in Canada, for linking it to your page!).