“You will find ambiguity a great ally on your road to power. Give a sign of Slytherin on one day, and contradict it with a sign of Gryffindor the next; and the Slytherins will be enabled to believe what they wish, while the Gryffindors argue themselves into supporting you as well. So long as there is uncertainty, people can believe whatever seems to be to their own advantage. And so long as you appear strong, so long as you appear to be winning, their instincts will tell them that their advantage lies with you. Walk always in the shadow, and light and darkness both will follow.”

“Lies propagate, that's what I'm saying. You've got to tell more lies to cover them up, lie about every fact that's connected to the first lie. And if you kept on lying, and you kept on trying to cover it up, sooner or later you'd even have to start lying about the general laws of thought. Like, someone is selling you some kind of alternative medicine that doesn't work, and any double-blind experimental study will confirm that it doesn't work. So if someone wants to go on defending the lie, they've got to get you to disbelieve in the experimental method. Like, the experimental method is just for merely scientific kinds of medicine, not amazing alternative medicine like theirs. Or a good and virtuous person should believe as strongly as they can, no matter what the evidence says. Or truth doesn't exist and there's no such thing as objective reality. A lot of common wisdom like that isn't just mistaken, it's anti-epistemology, it's systematically wrong. Every rule of rationality that tells you how to find the truth, there's someone out there who needs you to believe the opposite. If you once tell a lie, the truth is ever after your enemy; and there's a lot of people out there telling lies.”

“You couldn't changed history. But you could get it right to start with. Do something differently the FIRST time around.This whole business with seeking Slytherin's secrets... seemed an awful lot like the sort of thing where, years later, you would look back and say, 'And THAT was where it all started to go wrong.'And he would wish desperately for the ability to fall back through time and make a different choice. Wish granted. Now what?”

“Most Muggles lived in a world defined by the limits of what you could do with cars and telephones. Even though Muggle physics explicitly permitted possibilities like molecular nanotechnology or the Penrose process for extracting energy from black holes, most people filed that away in the same section of their brain that stored fairy tales and history books, well away from their personal realities: Long ago and far away, ever so long ago.”

“People go funny in the head when talking about politics. The evolutionary reasons for this are so obvious as to be worth belaboring: In the ancestral environment, politics was a matter of life and death. And sex, and wealth, and allies, and reputation... When, today, you get into an argument about whether "we" ought to raise the minimum wage, you're executing adaptations for an ancestral environment where being on the wrong side of the argument could get you killed. Being on the right side of the argument could let you kill your hated rival![...]Politics is an extension of war by other means. Arguments are soldiers. Once you know which side you're on, you must support all arguments of that side, and attack all arguments that appear to favor the enemy side; otherwise it's like stabbing your soldiers in the back—providing aid and comfort to the enemy. People who would be level-headed about evenhandedly weighing all sides of an issue in their professional life as scientists, can suddenly turn into slogan-chanting zombies when there's a Blue or Green position on an issue.”

“Like that's the only reason anyone would ever buy a first-aid kit? Don't take this the wrong way, Professor McGonagall, but what sort of crazy children are you used to dealing with?""Gryffindors," spat Professor McGonagall, the word carrying a freight of bitterness and despair that fell like an eternal curse on all youthful heroism and high spirits.”

“It's a most peculiar psychology—this business of 'Science is based on faith too, so there!' Typically this is said by people who claim that faith is a good thing. Then why do they say 'Science is based on faith too!' in that angry-triumphal tone, rather than as a compliment? And a rather dangerous compliment to give, one would think, from their perspective. If science is based on 'faith', then science is of the same kind as religion—directly comparable. If science is a religion, it is the religion that heals the sick and reveals the secrets of the stars. It would make sense to say, 'The priests of science can blatantly, publicly, verifiably walk on the Moon as a faith-based miracle, and your priests' faith can't do the same.' Are you sure you wish to go there, oh faithist? Perhaps, on further reflection, you would prefer to retract this whole business of 'Science is a religion too!”