Types of Flaws

Causation/correlation

This is an important type of overlooked possibility, in which the arguer takes two things that happen at the same time (correlation) and concludes that one of those things caused the other (causation). The arguer overlooks two important possibilities: 1) a third, unaccounted-for thing could actually be the cause, and 2) the cause-and-effect could actually be in the reverse order of what the arguer believes. Example: Last summer, ice cream sales decreased while homicide rates more than doubled in this region. We should look into selling more ice cream in order to keep people safer.

Sampling

The arguer draws a general conclusion based on what's true about an inappropriate or biased sample. Example: Everyone I know wants to quit their job, so this country is headed for an employment crisis.

Ad hominem

The arguer attacks another arguer instead of the argument itself. The identity or motives of an arguer don't affect the validity of that person's argument. Example: My doctor tells me it's bad for your lungs to smoke cigarettes, but I know he's lying. I saw him furtively smoking a cigarette the other day.

Quantity versus percent

The arguer treats quantities and percents of something as if they're interchangeable, but percents by themselves don't tell you anything about actual numbers. Example: 10% of the people with Disease X died last year, whereas 50% of the people with Disease Y died last year. Clearly, Disease Y is hurting our population growth more than Disease X is. (But what if 1,000,000 people had Disease X and only 4 people had Disease Y?)

Lack of evidence as proof

The arguer takes a lack of evidence for a conclusion as if that conclusion is definitely wrong. Also known as taking an absence of evidence for "evidence of absence". Example: Alien life has never been discovered, so it's clear that alien life doesn't exist.

False dichotomy

The arguer acts like there are only two choices, when in fact it isn't an "either/or" situation. Example: If you're not with us, then you're against us. The arguer is overlooking the possibility that someone could remain neutral.

Possible vs. certain

The speaker assumes that because something is possible, then it'll happen. Example: Last year we didn't have enough budget money for employee raises, but this year there's plenty of money in the budget. So, it's clear that the company will give out raises this year.

Circular reasoning

Also known as "begging the question", circular reasoning is when the arguer assumes that his or her conclusion is already true when attempting to prove that same conclusion. Example: Duplicity is an unattractive characteristic, since it's repulsive to lie and deceive.

Equivocation

The arguer uses a potentially ambiguous term in more than one sense and consequently misleads the reader. Example: A feather is light , and what's light can't be dark, so a feather can't be dark.