OK, boys, girls, and any ancient aliens stopping by Earth for a return visit, time for another critical thinking spotlight, starting with a few more formal fallacies. We are concerned with the argument’s form, not its content. It is possible to use correct premises, reach a correct conclusion, and still commit a logical fallacy.

The classic form of argument goes major premise-minor premise-conclusion. Used correctly, it looks like this:

No men are women.
Lyle is a man.
Therefore, Lyle is not a woman.

Here is an example of it being used incorrectly, in the form of the fallacy of exclusive premises :

No men are women.
Some women are not electricians.
Therefore, some electricians are not men.

Every line here is correct, but the logic remains flawed. There is nothing in either premise that supports the conclusion. The distinction between men and women has no relevance to what percentage of men work as electricians. A key point is that two negative premises can never equal a conclusion.

Building a point in this way requires limiting the terms to three. In the four-term fallacy, an extraneous element is introduced, usually by way of equivocation. This is using the same word, but with a different meaning both times, such as this:

Nothing is more important than good health.
A corndog is better than nothing.
Therefore, a corndog is better than good health.

In the major premise, “nothing” is used to indicate the premium value of good health. In the minor premise, it is used to establish that a corndog’s value is more than zero.

A related fallacy, the quantifier shift, occurs when quantifiers are wrongly transposed. For example:

“Everybody has something to believe in. Therefore, there is something that everybody believes in.” It is true that every person believes is some type of idea, but not true that there is a specific concept that everyone adheres to.

Next, consider the proof by example, in which one or two examples are presented as proof of a broader statement. Entire conspiracy theories are built on this faulty premise. It is also common in political and social discourse. You might see it in this form:

“Pol Pot and Joseph Stalin committed mass murder, so atheists are responsible for genocide.” In the interest of balance, it could also be, “94 percent of Nazi Germany was Christian; therefore followers of Jesus endorse the Holocaust.”

Now we’ll tackle some informal fallacies. These are arguments whose premises fail to support the conclusion. These usually involve a problem with reasoning in addition to logical structure flaws.

One of the more common is Begging the Question, also known as Circular Reasoning. This happens when the speaker attempts to prove something that is included in the initial premise of an argument. Put another way, a proposition which requires proof is assumed without offering this proof.

As Aristotle said, “Begging or assuming the point at issue consists of failing to demonstrate the required proposition.” That pretty much says the same thing as above, but I wanted to reference a Greek philosopher to seem more impressive. Anyway, here is some question-begging:

“Children’s memories of previous lives confirm the existence of past lives because there would be no other source for these memories.”

The conclusion is that past lives exist. However, the premise starts with the same assumption. Saying the memories could have no other source than a past life is assuming past lives exist. The speaker has to argue for this, not be conceded the point.

Another example would be, “’President Reagan was a great communicator because he had the knack of talking effectively.” Great communicator and talking effectively are synonymous. Using one to support the other is circular reasoning. To support the claim, the speaker should say something like, “Ronald Reagan could articulate complex ideas in simple terms, which is one of the reasons he was a great communicator.”

Now we’ll consider the hasty generalization, in which one reaches a conclusion based on insufficient evidence. “I know a guy who has driven drunk nine times and never hurt anyone, so it’s safe.” It is unreasonable and dangerous to conclude drunk driving is safe, based on the experiences of one person out of six billion.

Also, be wary of survey results. They could be based on sample size that is too small. Or they could be selectively chosen from one out of 100 surveys that had desirable results. Or the result could be cherry picked, where other findings in the same survey are ignored for their inconvenience.

Phrasing is also crucial. This was demonstrated when caller ID was about to become commercially available. Surveys revealed either overwhelming support or overwhelming opposition, depending solely on if the question was, “Would you like to have the number of the person calling you displayed,” or “Would you like to have your number displayed when calling someone?”

We will close with the Red Herring, which is one of the easiest fallacies to spot and involves skirting the issue. Debates about whether President George W. Bush had blundered by invading Iraq often devolved into, “We need to support the troops,” which was irrelevant to the question. The Red Herring often displays a lack of responsibility, as in, “I got a ticket for fishing out of season. Don’t the cops have real criminals to focus on?” Or, “I’m not getting enough people to my skeptic blog because of these people believing in ghosts and ESP.”