I’m an engineer, so I get in a lot of debates. I get in lots of debates on a wide variety of other topics as well. I can certainly come across as argumentative, but all I’m really seeking is a reasonable debate between valid arguments.

What I often get, instead, are arguments that are really based on nothing. I think it’s important for people in our field to understand the more common logical fallacies so they can learn when to recognize them being used… and avoid using them themselves.

#5: Slippery Slope

This is a form of ‘probability fallacy’… i.e. because X has happened 10 times in the past, it is very likely to happen in the future. This, statistically, is false. If I flip a coin 10 times and get heads, it’s still 50/50 to get heads the eleventh time.

It’s hard to convince people that this isn’t a good argument, but it isn’t. In some cases, it’s an argument about the failings of human nature. But I still think it’s just lazy… tell me why it’s a bad idea rather than convince me that, at some point in the future, it will cause bad things to happen. I am sometimes guilty of this one myself.

Example: But it we add that property to the class to solve that problem, what stops us from adding other properties? Eventually, the class will have 1000 properties!

#4: Appeal to the Masses

Also known as an ad populum argument. Just because 10 ba-jillion people do it doesn’t mean it’s right. We used to bleed people to cure diseases… that didn’t make it right. Tell me what’s good about your solution. What are it’s pros and cons? I don’t care… at all… how many people think it’s a good idea.

Example:  But everyone is using Java applets on their web pages, so we should be doing that also!

#3: Appeal to Authority

Very, very common in this internet age to become victim to this one because authority is granted upon the most random of internet characters. Having a blog does not make you an authority, in any case, and it certainly isn’t a valid argument to point to anyone to validate your solution. If you want to plagiarize that person’s arguments to make your case, that’s fine… but please don’t tell me you’re right because some guy said so.

Example:  But Scott Hanselman says that everybody should be using NuGet for everything!

#2: Straw Man

This one is used a lot and it’s good to be able to spot it when it happens. Someone takes your side of the argument, misrepresents it in the most gross way possible in order to beat it about the head and shoulders like a birthday pinata.

Example: So you want to take all that data, jam thousands of rows in the database and then just do it all with stored procedures?!? Um, no… not what I said at all.

#1: Ad Hominem

This happens all the time. Basically attacking the debater rather than the idea. This is usually a desperation move or commonly used by someone unaccustomed to defending their positions. Often takes the form of Appeal to Motive…. attacking the debater by questioning their motives.

Example:  You don’t like this solution because you just don’t understand it (because, presumably, I am an idiot). You just want to do it that way because it’s less work for you and more work for me (appeal to motive).

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I think it’s good for people to know debating skills and what makes for a good argument, and what doesn’t. A good read of Robert’s Rules of Order would be nice also!