Ah, logic. The most beloved tool of hack sci-fi writers and Sheldon Cooper. You will not find any of it in here. This, rather, will contain a brief listing of common fallacies you’ll find during your stay with us here on the Interweb.
I should note that I’m not actually a logician or philosopher. I’m just a guy with time on his hands.
Appeal to authority
Structure: “Ah, but when discussing [subject not related to science], [respected scientist] said this…”
We tend to assume that famous or smart people know more about all subjects than we do. This is probably because, as a group, we are silly. [cue the late Graham Chapman in a colonel’s uniform]
Argument ad hominem
Structure: “We can’t trust Steve to come up with good homebrew for D&D. He’s got a big nose.”
Reason? Who needs it? Just haul up one of your opponent’s negative traits and act as though that totally disqualifies him from being listened to or having a point. While it may, in some circumstances, be relevant – “who are you to call me on drinking, you wake up hungover five nights a week” – it is rarely made along these lines and generally takes the form of “you are a bad X because of irrelevant trait Y”.
Argument ad nauseam
Structure: “But Tau are the best army.” [repeat 40 000 times]
If you can’t win through logic, go for victory through exhaustion. If everyone else is heartily sick of the argument, they will either withdraw in disgust or give in just to shut you up.
Correlation and causation
Structure: “So she never learned to pole dance, and then someone drove a 4WD through her house. Therefore, everyone should learn to pole dance to prevent people driving 4WDs through their houses.”
You can get some very weird results when you assume all correlated things are linked. My age, for example, is correlated with inflation. In a correlation/causation argument, if inflation was therefore stopped, I would never age another day.
Structure: “They’re not keeping 3e Infernals the same, so they’re obviously changing everything about them.”
The absolute essential trick to this one is to completely ignore any degree of subtlety. We’re talking levels of black and white that would make the average Steve Ditko character stare slack-jawed at you. Once you’ve got that down, you should be able to apply this with no qualms whatsoever.
Structure: “Bob says all scientists are space lizards. Andy says no scientists are space lizards. I guess this means half of all scientists are space lizards.”
When two people say precisely opposite things, many will try and harmonise them by assuming the truth lies somewhere in between. Fact checking is hard, after all.
Structure: “Ah, but you see, Darwin said [thing that meant exactly the opposite in context].”
A mutant form of appeal to authority, the first step in a good quote mine is to find a quote that, if all that icky “context” stuff was scraped off, would support your point. Then scrape off the context and print it. Movie reviews do this all the time by delicately expunging all the negative parts and replacing each with an ellipsis.
Reductio ad absurdum
Structure: see every example on this page
It’s OK when I do it, because I’m trying to exaggerate things for humorous purposes. Really.
Structure: “If we raise the speed limit by 5km in that area, soon the entire state will have 200km/hr school zones.”
The trick to a good slippery slope argument is to assume that everyone else on Earth is totally devoid of a sense of proportion and obviously can’t be trusted to tell the difference between raising taxes by 1% and raising them by 111%, or between legalising abortion and legalising the hunting of poor people for sport. Once you’ve internalised the knowledge that nobody else can be trusted to recognise “too far”, you can now make these arguments all you like.
Structure: “The New Testament God is all rainbows and kittens. The Old Testament God is all wrath and smiting. Thus, the Old Testament God is a tribe of RENEGADE SPACE CANNIBALS!” (1)
It is impossible to argue with the logic in these arguments, since there isn’t any. If you’ve seen the Chewbacca Defence episode of South Park, you’ll be familiar with the basic idea: to confuse your enemies so much they withdraw immediately.