Logical Fallacies

Have you ever heard an argument or a statement that was presented as fact, that just didn't ring true?

Perhaps the statement seemed to jump to a wild conclusion, or the argument being presented was based on evidence that couldn't easily be validated or was out of context.

These kinds of statements are often referred to as Logical Fallacies. Essentially, an argument that is built on flawed reasoning, and that – when you apply logic – is discovered to be false.

Logical fallacies can be persuasive, and are often used in rhetoric to encourage people to think a certain way or believe certain things. This is why we need to be careful and question the things we hear that don't quite "ring true."

In this article, we'll learn more about the different types of logical fallacies that can be used, what they are, and how to spot them. 

What Are Logical Fallacies?

A logical fallacy is a statement that seems to be true until you apply the rules of logic. Then, you realize that it's not. Logical fallacies can often be used to mislead people – to trick them into believing something they otherwise wouldn't.

Think, for example, about the statement below:

"In a study designed by a famous academic to test the effects of pleasant imagery on motivation, employees were shown images of baby animals and beautiful nature scenes for their first five minutes at work.

"Amazingly, results showed a 10 percent leap in profits in the first quarter and record earnings over the course of a year. So, showing employees pleasant images is a great way to increase their motivation and improve productivity."

What do you think about the argument you just read? Do you believe the conclusion?

You shouldn't.

The argument contains a number of logical fallacies. But don't worry if you believed the conclusion: the passage contains some very common (and effective) tactics for manipulating reason and logic.

The ability to discern a valid argument from a false one is an important skill. It's a key aspect of critical thinking   , and it can help you to avoid falling prey to fake news   .

If you're taken in by a logical fallacy, false conclusions might cause you to make decisions that you later regret. And using a logical fallacy in your own arguments can make you look gullible or uninformed. Worse still, it can make you seem dishonest.

Now let's examine some of the most common logical fallacies that people use, so that you can recognize them and understand how to contest them if you come across them.

Logical Fallacies Examples

Remember the example above? It relied on two of the most common logical fallacies: appeals to authority and false inductions. Let's look at both in more detail.

Appeals to Authority

This is where you rely on an "expert" source to form the basis of your argument. In the example presented above, the apparently expert source is "a famous academic." Mentioning an academic tends to imply authority and expertise, and that your argument is backed up by rigorous research. The effect is even stronger when you use a real name.

But name-dropping alone is not enough to "prove" your case. Even if the academic is real, and their research is genuine, it may not necessarily support your argument – it may be misquoted, misunderstood, taken out of context, or contain important caveats that undermine the point you are trying to make.

Try not to rely too heavily on a single expert's authority, or on a single source of data.

False Inductions

A false induction is often called a "non sequitur," which translates from Latin to "it does not follow." This fallacy gets you to infer a causal relationship where none is evident. Just because something happened before something else does not mean that there is a logical, causal link between the two.

In our example, showing pleasant images to the employees may or may not be linked to the company's improved performance. Many other factors could have been involved.

It also concludes that improved productivity is the result of increased motivation. This is another false induction. Whether or not the pleasant images had a direct impact on motivation, and therefore productivity, is not demonstrated in the example at all.

Other Common Logical Fallacies

The above example uses two types of fallacy, but there are many other logical fallacies that you may have come across in your place of work or more generally. Here are six other common logical fallacies.

The Slippery Slope

The slippery slope argument relies on making you think that the worst that can happen will actually happen, if you take a particular course of action. Of course, this is not necessarily the case.

This kind of argument crops up often. But, on closer inspection of the example, you can see that it's illogical to conclude that you will have to give absolutely everyone an afternoon off, every single week, just by allowing one employee to leave early one time.

The Bandwagon Fallacy

Here, you are led to believe in an idea or proposition simply because it's popular or has lots of support. But the fact that lots of people agree with something doesn't make it true or right   .

In fact, you need to ask some further questions before you can draw any kind of conclusion from an informal survey such as this.

For example: who were these people? Would they actually purchase something from the store at 2 a.m.? If so, how often? What are the costs versus the benefits   of such a plan?

At the same time, keep in mind that, just because lots of people believe in something doesn't mean it isn't true. Always try to think critically and don't be led by forceful arguments.

The False Dichotomy Fallacy

The false dichotomy fallacy depends on an "either-or" argument: you provide only two options and force people to choose between them. In fact, neither choice may be the best, and there may be many other options available. But the argument makes it look like the suggested option is the only feasible one.

In this example, there are almost certainly other options that the Board could consider. And is raising capital even the answer to improving or maintaining the company's competitive position?

The Straw Man Fallacy

The straw man fallacy involves creating a false argument and then refuting it. The counterargument is then believed to be true. By misrepresenting an opposing position (and then knocking it down) your own preferred position appears stronger.

By arguing that the proposed changes are an attack on motorists, the opponent has knocked down the position much more easily than if they tried to address the actual concerns the proposal is dealing with – in this case, a spike in fatalities due to traffic collisions and pollution levels.

The No True Scotsman Fallacy

Sometimes called an "appeal to purity," this is a way to dismiss flaws in an argument, or criticisms of it.

No matter how compelling the counterargument may be, the person committing this fallacy "moves the goalposts," and shifts the terms of the argument so that the contradictory evidence does not apply.

Observational Selection

This means that you draw attention to the positive aspects of an idea and ignore the negatives. You are trying to make your argument more persuasive by providing only half the story.

What this argument fails to address is the cost and return on investment of TV commercials versus radio. Does the 38 percent increase in retention translate to sales conversions? What percentage of radio listeners versus TV watchers actually buy the product?

It's easy to slip into observational selection if you become attached to an idea, especially if you were involved in generating it.

The "statistics of small numbers" fallacy is a similar concept. Here, you take one observation and use it to draw a general conclusion.

For example, "I would never use Gaudi Brothers to supply our paper products. My wife's company used them and they short-shipped products and back-ordered them."

This opinion is based on one bad experience, and it doesn't necessarily mean the company is always unreliable. Perhaps the purchasing company was late submitting orders or late paying their invoices.

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How to Avoid Logical Fallacies

To spot logical fallacies, you need a basic understanding of how an argument works. In logic, an argument is a set of statements where one statement is inferred from the other (or others). There are two types of statements:

• Premises are statements offered to provide evidence for the conclusion of an argument.
• Conclusions are statements that are inferred from the evidence provided.

For an argument to be valid or logical, the premises must fully support the conclusion. They do this in one of two ways:

1. Using Deductive Reasoning

Here you start with general premises and reach a specific, certain conclusion.

2. Using Inductive Reasoning

Here you start with specific premises and reach a generalized conclusion. This "bottom-up" logic uses premises to reach a conclusion that is probable, but not certain. (Read our article on Inductive Reasoning   for more on this.)

To check whether an argument presented to you has a firm grounding in logic, apply these two tests. If it passes, you can be confident that the argument is sound. If it doesn't, ask for more information and supporting evidence.

Infographic

You can see our infographic on Logical Fallacies here: