Logic 101: Two Fallacies of Presumption, Part 12 (of 12)

To revise a famous line from The Godfather: “Keep your friends close, but the laws of logic closer!”

In this final article in the series I will address a couple of informal fallacies that can potentially stand in the way of solid and successful critical thinking.

Fallacies of Presumption

Since logic is about proving (or verifying) things through the use of arguments, presumption can be a big problem. The truth of the conclusion of an argument shouldn’t be presumed. Rather a good argument offers evidence, facts, or reasons to support the conclusion being drawn. There is a whole series of particular fallacies that fall under this category. Let’s examine two:

1. Wishful Thinking:

The logical error of wishful thinking consists in assuming that because we want a particular thing to be true, it must be true (or assuming that because we don’t want something to be true, it isn’t). The problem occurs when the “wishing” is treated as support for the desired conclusion. However, mere wishing doesn’t make something either true or false.

This fallacy is easy to commit because people often desire or are attracted to a specified outcome. But wanting something in and of itself isn’t necessarily evidence. Good arguments must have genuine evidence that support the conclusion. Christian author C. S. Lewis has presented an “argument from desire” in his apologetic writings but that argument is in reality an attempt to provide the best explanation for why human beings have basic desires to begin with. Thus, Lewis’s argument does not involve the wishful thinking fallacy.

2. Begging the Question:

This fallacy engages in “circular reasoning.” Begging the question occurs when an argument either (a) conceals an essential premise, or (b) bases a premise (the support) on the truth of the as yet unproved conclusion (the central claim). In the first form, the supporting premise is assumed rather than reasonably supported. In the second, the conclusion supports the premise instead of the other way of around.

Models of a Logical Argument

Argument = Support (premises) + Central Claim (conclusion)

Good Argument (sound or cogent) = Support (premises) that genuinely infer or back the central claim (conclusion)

The study of logic helps us organize our thinking and, thus, to arrive at reasonable and truthful conclusions. There is nothing more important than thinking clearly and carefully about truth and reality. And from a biblical standpoint, such thinking brings honor to God who gave human beings such remarkable cognitive faculties through the imago Dei (image of God, Genesis 1:26-27).

For more about the importance of logic and critical thinking, see my book A World of Difference: Putting Christian Truth-Claims to the Worldview Test. For a great handbook in dealing with logical fallacies, see Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments by T. Edward Damer.

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