Article: Fallacies of Omission (Dr. L. Kip Wheeler)

Logical Fallacies Handlist: Arguments to Avoid When Writing

FALLACIES OF OMISSION: These errors occur because the logician leaves out necessary material in an argument or misdirects others from missing information.

Stacking the Deck: In this fallacy, the speaker "stacks the deck" in her favor by ignoring examples that disprove the point and listing only those examples that support her case. This fallacy is closely related to hasty generalization, but the term usually implies deliberate deception rather than an accidental logical error. Contrast it with the straw man argument.

‘No True Scotsman’ Fallacy: Attempting to stack the deck specifically by defining terms in such a narrow or unrealistic manner as to exclude or omit relevant examples from a sample. For instance, suppose speaker #1 asserts, “The Scottish national character is brave and patriotic. No Scottish soldier has ever fled the field of battle in the face of the enemy.” Speaker #2 objects, “Ah, but what about Lucas MacDurgan? He fled from German troops in World War I.” Speaker #1 retorts, “Well, obviously he doesn’t count as a true Scotsman because he did not live up to Scottish ideals, thus he forfeited his Scottish identity.” By this fallacious reasoning, any individual who would serve as evidence contradicting the first speaker’s assertion is conveniently and automatically dismissed from consideration. We commonly see this fallacy when a company asserts that it cannot be blamed for one of its particularly unsafe or shoddy products because that particular one doesn’t live up to its normally high standards, and thus shouldn’t “count” against its fine reputation. Likewise, defenders of Christianity as a positive historical influence in their zeal might argue the atrocities of the eight Crusades do not “count” in an argument because the Crusaders weren’t living up to Christian ideals, and thus aren’t really Christians, etc.

Argument from the Negative: Arguing from the negative asserts that, since one position is untenable, the opposite stance must be true. This fallacy is often used interchangeably with Argumentum Ad Ignorantium (listed below) and the either/or fallacy. For instance, one might mistakenly argue that, since the Newtonian theory of mathematics is not one hundred percent accurate, Einstein’s theory of relativity must be true. Perhaps not. Perhaps the theories of quantum mechanics are more accurate, and Einstein’s theory is flawed. Perhaps they are all wrong. Disproving an opponent’s argument does not necessarily mean your own argument must be true automatically, no more than disproving your opponent's assertion that 2+2=5 would automatically mean your argument that 2+2=7 must be the correct one.

Appeal to a Lack of Evidence (Argumentum Ad Ignorantium, literally "Argument from Ignorance"): Appealing to a lack of information to prove a point, or arguing that, since the opposition cannot disprove a claim, the opposite stance must be true. An example of such an argument is the assertion that ghosts must exist because no one has been able to prove that they do not exist.

Hypothesis Contrary to Fact (Argumentum Ad Speculum): Trying to prove something in the real world by using imaginary examples alone, or asserting that, if hypothetically X had occurred, Y would have been the result. For instance, suppose an individual asserts that if Einstein had been aborted in utero, the world would never have learned about relativity, or that if Monet had been trained as a butcher rather than going to college, the impressionistic movement would have never influenced modern art. Such hypotheses are misleading lines of argument because it is often possible that some other individual would have solved the relativistic equations or introduced an impressionistic art style. The speculation might make an interesting thought-experiment, but it is simply useless when it comes to actually proving anything about the real world. A common example is the idea that one "owes" her success to another individual who taught her. For instance, "You owe me part of your increased salary. If I hadn't taught you how to recognize logical fallacies, you would be flipping hamburgers at McDonald's for minimum wages right now instead of taking in hundreds of thousands of dollars as a lawyer." Perhaps. But perhaps the audience would have learned about logical fallacies elsewhere, so the hypothetical situation described is meaningless.

Complex Question (Also called the "Loaded Question"): Phrasing a question or statement in such as way as to imply another unproven statement is true without evidence or discussion. This fallacy often overlaps with begging the question, since it also presupposes a definite answer to a previous, unstated question. For instance, if I were to ask you “Have you stopped taking drugs yet?” my hidden supposition is that you have been taking drugs. Such a question cannot be answered with a simple yes or no answer. It is not a simple question but consists of several questions rolled into one. In this case the unstated question is, “Have you taken drugs in the past?” followed by, “If you have taken drugs in the past, have you stopped taking them now?” In cross-examination, a lawyer might ask a flustered witness, “Where did you hide the evidence?” or "when did you stop beating your wife?" The intelligent procedure when faced with such a question is to analyze its component parts. If one answers or discusses the prior, implicit question first, the explicit question may dissolve.

Complex questions appear in written argument frequently. A student might write, “Why is private development of resources so much more efficient than any public control?” The rhetorical question leads directly into his next argument. However, an observant reader may disagree, recognizing the prior, implicit question remains unaddressed. That question is, of course, whether private development of resources really is more efficient in all cases, a point which the author is skipping entirely and merely assuming to be true without discussion.

V. A Useful Tool in Logic: Occam's Razor

The term "Occam's Razor" comes from a misspelling of the name William of Ockham. Ockham was a brilliant theologian, philosopher, and logician in the medieval period. One of his rules of thumb has become a standard guideline for thinking through issues logically. Occam's Razor is the principle that, "non sunt multiplicanda entia praeter necessitatem" [i.e., "don't multiply the agents in a theory beyond what's necessary."] What does that mean? If two competing theories explain a single phenomenon, and they both generally reach the same conclusion, and they are both equally persuasive and convincing, and they both explain the problem or situation satisfactorily, the logician should always pick the less complex one. The one with the fewer number of moving parts, so to speak, is most likely to be correct. The idea is always to cut out extra unnecessary bits, hence the name "razor." An example will help illustrate this.

Suppose you come home and discover that your dog has escaped from the kennel and chewed large chunks out of the couch. Two possible theories occur to you. (1) Theory number one is that you forgot to latch the kennel door, and the dog pressed against it and opened it, and then the dog was free to run around the inside of the house. This explanation requires two entities (you and the dog) and two actions (you forgetting to lock the kennel door and the dog pressing against the door). (2) Theory number two is that some unknown person skilled at picking locks managed to disable the front door, then came inside the house, set the dog free from the kennel, then snuck out again covering up any sign of his presence, and then relocked the front-door, leaving the dog free inside to run amok in the house. This theory requires three entities (you, the dog, and the lockpicking intruder) and several actions (picking the lock, entering, releasing the dog, hiding evidence, relocking the front door). It also requires us to come up with a plausible motivation for the intruder--a motivation that is absent at this point.

Either theory would be an adequate and plausible explanation. Both explain the same phenomenon (the escaped dog) and both employ the same theory of how, i.e., that the latch was opened somehow, as opposed to some far-fetched theory about canine teleportation or something crazy like that.

Which theory is most likely correct? If you don't find evidence like strange fingerprints or human footprints or missing possessions to support theory #2, William of Ockham would say that the simpler solution (#1) is most likely to be correct in this case. The first solution only involves two parts--two entities and two actions. On the other hand, the second theory requires at least five parts--you, the dog, a hypothetical unknown intruder, some plausible motivation, and various actions. It is needlessly complex. Occam's basic rule was "Thou shalt not multiply extra entities unnecessarily," or to phrase it in modern terms, "Don't speculate about extra hypothetical components if you can find an explanation that is equally plausible without them." All things being equal, the simpler theory is more likely to be correct, rather than one that relies upon many hypothetical additions to the evidence already collected.

Copyright Dr. L. Kip Wheeler. Permission is granted for non-profit, educational, and student reproduction.

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