Logic and critical thinking are lost arts in American public discourse, and much of American private life, because public education never really broaches the topic. The following article offers college-level knowledge on logic and critical thinking.

Deductive Reasoning

The most common method of building an argument is deductive reasoning, where a syllogism is constructed using a major premise, a minor premise and a conclusion. In most cases, the major premise is the all-encompassing, worldview idea, while the minor premise is the idea specific to a given argument. The conclusion then naturally follows from the two premises.

For example, in an essay arguing that handguns should be outlawed, the syllogism might look like this:

• Major Premise: That which is potentially dangerous should be outlawed.
• Minor Premise: Handguns are potentially dangerous.
• Conclusion: Handguns should be outlawed.

When evaluating the merits of a deductive syllogism, the critical thinker needs to ask if an argument is sound. That is, are the premises true (do you agree?) and are the premises valid (do they relate to each other?). If the syllogism is either false or invalid, then the argument is unsound.

Methods of Evidence

Once an argument is constructed using deductive reasoning, the author needs to determine how they will support their argument. Here are a few acceptable methods of evidence.

• Experimentation: Experiments are exercises conducted in a controlled environment to evaluate a hypothesis. For example, if someone wanted to prove that Drug X cured cancer, they would recruit two groups, give one group the drug, and another group a sham therapy. If the treated group showed improvement, the author could then persuade his audience that the drug was effective.

• Real Events: These are situations that have actually occurred either in history or in the realm of current events. For example, if someone wanted to prove that handguns are dangerous they might cite several events where children were accidentally shot in their homes.

• Hypotheticals: These are situations that have not yet happened, but could. For example, if someone wanted to prove that the death penalty was immoral they could present a hypothetical situation where an innocent man was wrongly accused, sent to death row and executed.

• Analogies: An analogy is when an author tries to convince his audience that the situation on which they are opining is similar to one where the desired outcome was achieved. For example, if someone wanted to prove that the failure to legalize gay marriage is a moral failure, they might draw an analogy to the period in American history where African Americans were not allowed to marry each other or to marry whites.

• Authoritative Testimony: This is when a persuader cites a recognized authority in a field who supports their point of view. For example, if an author is trying to make a point about a matter of law they might quote a law professor. If the author was trying to make a point about religion, they might quote a member of the clergy.

• Statistics: Statistics are a measurement typically expressed as a percentage. For example, if a persuader was trying to convince the reader that fast food leads to obesity they might cite a statistic that shows 80 percent of Americans who consumed fast food twice a week gained 20 extra pounds in a year.

Nonrational Appeals

In addition to the recognized forms of evidence, there are two common nonrational appeals that can be persuasive. However, it is risky to use these methods exclusively.

• Emotional Appeals: Persuaders who want to get their audience's attention will sometimes use an example that provokes an emotional response. For example, when making a point about education, a persuader who wants to use an emotional appeal is more likely to describe the advantages for children rather than administrators.

• Reductio ad Absurdum: This is a Latin term that means reducing an argument to its absurd conclusion. For example, someone who wanted to make a point against equal rights might argue that we would soon be unable to assume someone's gender.

Logical Fallacies

In arguing and persuading there are rules, and the following logical fallacies are common examples of ways those rules are often broken.

• Oversimplification: This is when a persuader jumps to a conclusion without considering nuance. For example, to simply state "poverty causes crime," is an oversimplification because while it is true that crime exists in poverty stricken areas that is not necessarily evidence of causality as many people are poverty stricken but not criminals.

• False dichotomy: This is when a persuader presents only two choices with one being an obviously bad option, and offers no potential third way. For example, someone arguing against corporal punishment might say, "we can choose between time outs or child abuse." This is a false dichotomy, however, because they have not considered the parents who administer corporal punishment in loving, effective ways.

• Ad Hominem Attack: This is when a persuader attacks the source of an argument rather than the content. For example, if in a debate about the legalization of marijuana one claimant accused the other claimant of beating his wife he might get a shocked response from the audience but he will also have committed a logical fallacy.

• The Slippery Slope: This is when a persuader suggests a negative future that does not logically flow from the current situation. For example, when arguing about handguns, a persuader invoking the slippery slope might say, "if you are going to outlaw handguns for safety reasons you will eventually have to outlaw automobiles."

• Appeal to Ignorance: This is when a persuader invokes some variation of, "yes, but, we might never know what would happen if..." While it is a good rhetorical device, the fact that something has in fact not happened negates its evidentiary value.

• Protecting the Hypothesis: This is when a persuader considers only their side of an argument without offering an analysis of the opposing position. One-sided arguments are logical fallacies.