For those of you experiencing a Freudian moment, note that this word starts with an "F", not a "Ph"!
A fallacy is a deceptive argument. I suspect that the folks that use fallacies here on JavaRanch are not being deceptive intentionally.
I suppose there might be two ways to read this information:
1) Things to avoid doing because it makes you look like a jerk
2) Things to do because you can sucker dopes into doing things your way
Massive books can be written about fallacy, persuasion and debate. My purpose with this document is to point out the fallacies that I think are the biggest issues for software engineers. Mathematical logic, where most people struggle with fallacy, is something I rarely see software engineers struggle with.
If you ever find yourself using fallacies, maybe you should consider conceding your point. After all, if you had really good reasoning, would you stoop to using fallacies? I know that when I hear somebody using fallacies I'm pretty certain that their point is dead.
If you discover other people using fallacies, note that pointing out a fallacy is definitely going to earn you jerk points. In these cases, my advice is to stick to the high road, and ignore the fallacy as best you can. Hopefully the other people in the forum spotted the fallacy too.
Fallacy is a lot like Jedi Mind Tricks: They only work on the weak-minded. And of course, if you attempt to use a Jedi Mind Trick on somebody, you are essentially saying, "I think you are weak-minded enough to fall for my Jedi Mind Trick!" Kind of insulting really.
We are supposed to be professionals. The fallacies listed below should never happen in a professional environment.
Some people will jump to using a fallacy as a last ditch effort to save face. A good engineer will gracefully acknowledge that they have done their best to present a case and admit that the argument appears to be weak. Or that they have simply done their best to present their argument and there is nothing more to present.
Generally, the best approach to dealing with any fallacy you read is to ignore the fallacy part and try to acknowledge only the legitimate points.
And now I present my list of fallacies:
1) Proof by Abuse (ad Hominem Fallacy)
Your argument is wrong because you are a jerk!
Your argument is wrong because your mother dresses you funny!
Your argument is wrong because you went to a lame engineering school!
Your argument is wrong because I'm paid more!
Your argument is wrong because I have more experience!
Your argument is wrong because you're incompetent!
"I'm happy to discuss my being a jerk, but for now I would like to focus on..."
"I'm not sure how my mother dresses me applies to this topic."
2) Proof by Personal Offense
Your argument is wrong because I am personally offended by something in your argument.
"Is that some sort of slam because I'm Chinese?"
There's nothing like inadvertently sticking your foot in your mouth to learn about other cultures. Or about the sensitive spots of all sorts of personal issues. It sure derails a discussion. But for this to qualify as a fallacy, the offended party would be feigning offense to derail the argument.
Apologize profusely and try to get the discussion back on track. Don't be surprised if the offended party wants to avoid further discussion of an issue he was losing. He will favor discussing your alleged callousness.
3) Proof by Opinion as Fact
Your argument is wrong.
Your argument is wrong. Period.
This is usually done by somebody that is too weak minded to come up with something better. So they just say, "you're wrong" or "the only solution is..." They state it clearly and concisely as if there can be no alternative. It is as if they have the royal voice.
Often times, opinions are stated as facts as a form of exaggeration. Exaggeration is a fallacy.
"I think the world might be round!"
"The world is flat."
Ask, "I didn't know that that had been proven. Could you please enlighten me?" or "I was under the impression that that was a matter of opinion, yet you state it as a fact. Could you help me to understand why?"
A low road:
If this sort of thing is becoming a repeated problem, it might be good to pick one "fact" and focus on it until it can be clarified. The goal being to shame the person into not using this fallacy any more. Basically, this leaves the burden of proof in your corner, but if the person spouts these sorts of "facts" frequently, a real easy one should pop up at some point. "You state 'the world is flat' rather factually. Are you suggesting that this is a well known fact instead of just your opinion?"
4) Proof by Anecdote
Your argument is wrong because I once did it a different way.
In the late 70's Radio Shack sold a computer they called the TRS-80. Many people who bought this computer were certain that it was the best computer ever! Often, this certainty came without any knowledge of other computers! Sometimes these folks would insist on trying to build applications on a TRS-80 that were best left for mainframe systems. Some people called this ''Trash 80 Syndrome." And today I still hear the term used to describe an engineer that has done something one way in the past and is certain there is no other way. Donate now to help find a cure for this horrible disease among engineers!
"My solution may be inferior to the one you have experience with, but I would certainly feel better if I could at least tell you all about what's rattling about in my head before we finalize the decision."
5) Proof by Inflation (Slippery Slope Fallacy)
Your argument is wrong because your argument times a billion is wrong
If everybody did it, the world would end.
You should never drink alcohol because if you did, you wouldn't be able to stop, and then you would be die of liver disease.
6) Proof by Decency (Prejudicial Fallacy)
Decent people agree with my argument.
"Any reasonable person can see that this bill is too expensive!"
"Any decent person would stay off the grass."
We can combine the Prejudicial Fallacy with the Ad Hominem Fallacy quite easily:
"What kind of jerk would support any war?"
"Any decent person would stay off the grass.": "I suppose my decency could be debatable, but I still advocate playing on the grass!"
7) Proof by Dismissal
"So you concede the argument?"
8) Proof by Straw Man (Straw Man Fallacy)
Your argument is wrong because something similar is wrong.
"Organic apples are bad because I don't like apples with worms in them."
This is called the "Straw Man Fallacy" because you set up an obvious bad thing and then link the argument to the obviously bad thing. It's easy to beat up the obviously bad thing. Worms in apples are bad (unless you're a chicken - then the apple is good and the worm is better). Apples from a professional, organic orchard generally have the same worm count as apples from a professional, non-organic orchard: none. Yet the statement above really throws you off your feed, doesn't it! The mighty power of the straw man fallacy!
The straw man is probably one of the most common fallacies in use.
Embrace that the two are similar, but emphasize that they are not the same: "Nobody likes worms in their apples. I don't think there is a connection between organic apples and worms. Surely, apples that have received no care can be wormy. But many orchardists that care for their trees organically have happily reported that their apples have no worms!"
9) Proof by Limited Survey (Hasty Generalization Fallacy)
10) Proof by Analogy (False Analogy Fallacy)
11) Proof by Termination
Your argument is wrong because it is impossible and this conversation is over.
Your argument is wrong because I'm leaving in protest.
12) Proof by Volume (Appeal to Force Fallacy)
YOUR ARGUMENT IS WRONG BECAUSE I CAN TYPE IN ALL CAPS!
In case you didn't know, all caps is considered to be similar to yelling.
13) Proof by Profanity
14) Proof by Rolling Eyes
15) Proof by Past Crimes
16) Proof by Language Barrier
Your argument is wrong because your language is not my native language, and I'm hoping it is too much hassle for you to try again.
This is only a fallacy if the "confused" party is actually not as confused as they claim. After a few attempts to clarify, the "confused" party might even claim that the argument is weak if it is not easy to understand.
Patiently play along. Demonstrate that you can play this game as long as they are willing to play it.
17) Proof by Limited Options (False Dilemma)
Your argument is wrong because I will only consider two options and what you propose is not one of them.
You're either with us or against us! And you aren't with us ...
18) Proof by Vote (Bandwagon Fallacy)
My statement is fact because 51% agree with me.
This was the argument that Columbus faced when he tried to tell people that the world was round: "Everybody knows the world is flat."
19) Proof by Association
20) Proof by Tradition
My argument is right because we have always done it that way.
The Evil Banana
1) Place five gorillas in a cage.
2) Suspend a banana in the cage above a ladder.
3) When any gorilla attempts to use the ladder, wet all five gorillas with a fire hose.
4) When gorillas no longer attempt to use the ladder, replace one gorilla.
5) Note that when the new gorilla attempts to use the ladder, the other gorillas will beat him up. The fire hose is no longer needed.
6) Repeat step 4 until all original gorillas have been replaced.
7) Note that at this point, no gorillas use the ladder and none of them knows why.
There are two possible morals to this story:
1) Many people will prevent you from getting a perfectly good banana even though nobody knows why.
2) Many people will prevent you from getting a perfectly good banana for a very good reason, although nobody knows what that reason is.
21) Proof by Sarcasm
Oh sure, your argument is right.... And the pope's a Buddhist!
Tough issues are difficult enough to discuss without adding the misdirection of sarcasm. Rather than arguing against a statement, you have to argue against an implication. And it could be argued later that your interpretation of the implication was not accurate.
Try to state their implication and then wrestle with that: "I think your implication is...."
22) Proof by Mystery
Your argument is wrong because nobody has made that argument before.
Your argument is wrong because nobody has proven it to be true.
Your argument is wrong because nobody has proven the opposite to be false.
Nobody has proven that there is a Santa Claus; therefore there isn't a Santa Claus.
Nobody has proven that there is not a Santa Claus; therefore there is a Santa Claus.
23) Proof by Lame Jedi Mind Trick
Give me a break!
You have to be kidding!
It's amazing how this really does work on the especially weak-minded. That's what makes it especially insulting to the not-so-weak-minded.
Possible high roads:
"Give me a break": "I, too, would appreciate a break."
"Aw, c'mon": "Could you please clarify how this supports your argument?"
"You have to be kidding!": "I checked the floor for small goats. There are none. Thanks for asking."
24) Proof by Baby Talk
Yow awgument is wong because I've devewoped a baby-towk speech impediment.
Your argument is wrong because I'm... talking... slow... enough... for... stupid... people... to... understand...
25) Proof by Whining
26) Proof by Absent Expert (Appeal to Authority Fallacy)
Your argument is wrong because Woody Allen said so.
Of course, other equally qualified experts may have different views.
Another point is that sometimes it turns out that the expert never really said that!
27) Proof by Persistence (ad Nauseum Fallacy)
Your argument is wrong. Your argument is wrong. Your argument is wrong. Your argument is wrong. Your argument is wrong. Your argument is wrong. Your argument is wrong. Your argument is wrong...
This has been proven to be an amazingly powerful tool frequently used by politicians and advertisers.
28) Proof by Burden of Proof
Your argument is wrong because you have no proof. Therefore my argument is right (please overlook the fact that I have no proof either!)
"Prove it!" - amazing how two words can really take the wind out of your sails.
For further reading on the subject, refer to this article by Dr. Michael C. Labossiere