Fallacies of Weak Induction

Fallacies of weak induction occur not when the premises are logically irrelevant to the conclusion but when the premises are not strong enough to support the conclusion.

Appeal to Unqualified Authority

Mr. Turner, president of the Big Pine Lumber Company, has said that we should chop down all the redwoods and sell the timber to stimulate the local economy. In view of Mr. Turner's experience with the lumber business, it appears that we should indeed do this.

Omar the Magnificent, who is this country's greatest astrologer, says that the AIDS epidemic is caused by a perverse alignment of the planets, and that there is nothing anyone can do about it. therefore, we can only conclude that all of these efforts to find a cure for AIDS are a waste of time.

Though testimony sometimes does provide strong evidence in support of a conclusion, it does so only when the authority in question is trustworthy.

Authorities that are biased, not experts in the relevant fields, or not otherwise trustworthy cannot lend credible support to a conclusion.

Appeal to Ignorance

Nobody has ever proved the existence of ghosts. Therefore, we have alternative but to conclude that ghosts are mere figments of the imagination.

Occurs when premises of an argument offer in support of a conclusion the fact that nothing has been proved either way regarding the conclusion.

Exception 1: Sometimes qualified researchers do find no support for a conclusion after a reasonable amount of study. It may then be reasonable to infer that the conclusion cannot be supported.

Exception 2: In some legal systems no evidence presented one way or the other means the defendant is not guilty.

Hasty Generalization

A reporter in the local newspaper exaggerated her story just to make it appear more exciting, and a reporter on the evening news got his facts mixed up. Therefore, you can't trust anyone in the news media these days.

Occurs when an argument draws a conclusion about a group when the sample is inadequate to support the generalization, perhaps because it is unrepresentative or too small.

Hasty generalization is sometimes called "converse accident"

False Cause

Every time I take a shower, the telephone rings. Since I'm dying to talk to somebody right now, I should jump in the shower.

Occurs when the link between the premises and conclusion depends on a questionable causal connection.

Some arguments wrongly assume that just because one event precedes another the former caused the latter.

Some alleged causal relationships are spurious.

Sometimes the causal order is reversed.

Sometimes the cause is oversimplified.

Slippery Slope

The student association has asked that we provide condom machines on campus. this request is ridiculous. If these machines are installed, then more and more students will start engaging in premarital sex. This will lead to a complete erosion of morals, and soon the students will start lying and stealing. Rape, arson, and murder will soon become rampant. In the end, the campus will totally disintegrate.

Occurs when the conclusion rests upon an improbable chain reaction.

Weak Analogy

No one would blame a bartender for having a few drinks on the job. but an airline pilot is no less a human being than a bartender. So, no one should blame an airline pilot for having a few drinks on the job.

Occurs when an analogy upon which the argument depends is too weak to support the argument.