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Inductive Fallacy Study Guide (page 3)

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Updated on Apr 25, 2014

Post Hoc, Ergo Propter Hoc

When you read about the chicken-and-egg fallacy earlier in this lesson, you noted that just because one event precedes another doesn't mean that the first caused the second. To assume it does is another illogical fallacy known as post hoc, ergo propter hoc, Latin for, "after this, therefore because of this." Often shortened to just post hoc and sometimes referred to as false cause, this fallacy follows the pattern:

  1. Event A precedes event B.
  2. Event A caused event B.

But to make a strong causal argument, you must account for all relevant details. For example, every time Ahmed tries to open a video program on his computer, it crashes. He concludes that the program is causing the computer to crash. However, computers are complex machines, and there could be many other causes for the crashes. The fact that the opening of one program always precedes the crash is a good possibility for cause, but it cannot be maintained as the one and only cause until a stronger link is made. To avoid the post hoc fallacy, he would need to show that all of the many other possibilities for the cause of the crashing have been evaluated and proven to be irrelevant.

Superstitions are another example of post hoc fallacies. Some superstitions are widely held, such as "if you break a mirror, you will have seven years of bad luck." Others are more personal, such as the wearing of a lucky article of clothing. However, all of them are post hoc fallacies because they do not account for the many other possible causes of the effect. Bad luck could happen to someone who breaks a mirror, but bad things also happen to those who do not. In these cases of superstitions, the real cause is usually coincidence.

How can you strengthen an argument and keep it from becoming an example of the post hoc fallacy? First, show that the effect would not occur if the cause did not occur. For example, if I don't strike the match, it will not catch on fire. Second, be certain there is no other cause that could result in the effect. Are there any sources of flame near the match? Do matches spontaneously catch fire? Is there anything else that could cause it to catch fire? If the answer is no, then there is no post hoc fallacy.

Examples

  • I took three echinacea tablets every day when my cold started. Within a week, my cold was gone, thanks to the echinacea.
  • I wanted to do well on the test, so I used my lucky pen. It worked again! I got an A.
  • Last night I had a dream that there was a car accident in my town. When I read the paper this morning, I found out a car accident did happen last night. My dreams predict the future.

Tip

If you say that A causes B, have something more to say about how other than just that it came first! You might want to use data and statistics to make your point.

In Short

Inductive reasoning is used all the time to make generalizations from specifics. But it can be misused to create arguments for things such as racial prejudice and superstitions. These weak arguments involve fallacies such as hasty conclusions, chicken and egg, and composition (making a conclusion about a whole based on the qualities of its parts). Learning how to recognize such faulty reasoning will help you to avoid being tricked by it, and also help you avoid making such mistakes in your arguments.

Skill Building Until Next Time

  • Read the science section of your newspaper or a science article in a magazine and find an example of inductive reasoning. Check for fallacies. If none exist, come up with a way to apply one of the fallacies in this lesson to the example.
  • Remember that in order to determine cause, you must have enough evidence to support the conclusion. The next time you are blamed for something or hear someone blaming another person, think about this: Do they have strong premises on which to base their conclusion? Who or what could have been the real cause?

Exercises for this concept can be found at Inductive Fallacy Practice Exercises.

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