When you read a text whose purpose is to persuade or argue a point, you need to analyze that text to see whether the argument is logical. Logical arguments need to be reasonable; supported with appropriate, relevant evidence from valid sources; and based on acceptable assumptions. Knowing a bit about logical arguments will help you analyze a text intended to persuade, as well as write your own persuasive, logical arguments.
Logical Argument Basics
Main Idea, Content, Warrant
The claim is the author’s main argument—what the author wants you to do, think, or believe by the time you finish reading the text. The content is the evidence which provides the support and reasoning upon which the claim is built. The underlying assumption, the way the author uses the evidence to support the claim, often called the warrant. These three parts of a logical argument all need to be believable and coordinated for the argument to be valid. 
For example, the author’s main idea or claim may be this: Decreasing carbon dioxide emissions from car exhaust, manufacturing processes, fertilizers, and landfills, while slowing deforestation, may help slow the process of global warming. For this claim, the underlying assumption is that global warming is something that should be slowed. To support this claim and link the evidence with the claim, the author included the following types of content as evidence:
- Facts that show the linkage between increased carbon dioxide levels and warmer temperatures
- Statistics about temperature increases and their effects, and future projections based on current statistics
- Studies done showing that fuel emission laws enacted in a certain location cut down on carbon dioxide levels
- Citation of recognized experts in the field
- Testimony of those involved first-hand with the issue
In this example, all of the argument parts coordinate with one another. The evidence seems appropriate, and is especially strong if it comes from valid sources such as scientific studies published in peer-reviewed journals. The underlying assumption is supported by the evidence. As a reader analyzing the text, you could conclude that this is a logical argument.
On the other hand, the author’s argument may be this: Good nutrition should be taught in school rather than at home. For this claim, the underlying assumption might be that parents are not as good at teaching their children as trained teachers, or it might be that schools have more teaching resources than parents. To support this claim and link the evidence with the claim, the author included the following types of content as evidence:
- interviews with teachers
- interviews with school administrators
- statistics from studies done over time, showing that elementary school children who received lessons on good nutrition maintained good eating habits into adulthood more than those did not receive formal lessons
- personal interviews
In this example, it appears that the first warrant was in effect, based on the way the author linked claim and evidence. You might question the underlying assumption in the warrant, as many readers may not accept this belief. As an analytical reader whose purpose is to evaluate the text, you also might question the type of support. Teachers, school administrators, and people who were interviewed might be biased. Statistics on the effectiveness of teaching about nutrition in school do not track a comparative group of children who were taught at home, so the conclusions of the studies in this case might not fully relate to the argument. As a reader analyzing this text, you could conclude that the author’s argument is not logical.
As you analyze an argument, try to isolate, identify, and investigate these three aspects of argument—main idea, content, warrant—to evaluate the quality of the text.
Ethos, Pathos, Logos
Another complementary way to analyze an argument and evaluate a text is to investigate the three main types of appeals authors use to support their claim. These types of appeals are traditionally referred to by their Greek names: logos (appeal to logic), pathos (appeal to emotion), and ethos (appeal to authority).
Logical appeals may include facts, case studies, statistics, experiments, and expert testimony. Authoritative appeals may include citations of recognized experts and testimony of those involved first-hand in the issue. Emotional appeals may include personal anecdotes, stories, impact studies, and first-hand testimony. Many logical arguments rely on some combination of these three types of appeals. However, an argument may not be logical if a certain type of appeal does not coordinate with the claim, and/or if an author relies too heavily on emotional appeal, for example, to the exclusion of factual support.
The two videos below discuss how to apply these concepts to analyze an argument and thus evaluate a text.
When you analyze a text’s arguments in order to evaluate the quality of that text, you also need to determine whether the content contains errors in logic. Errors in logic, called logical fallacies, weaken the argument and thus the validity of the text. When readers spot questionable reasoning or unfair attempts at audience manipulation, more than their evaluation of the author’s argument (logos) may be compromised. Their evaluation of the credibility of the speaker (ethos), and perhaps their ability to connect with that speaker on the level of shared values (pathos), also may be compromised.
Types & Examples of Logical Fallacies
Classifying fallacies as errors of ethos, logos, or pathos may help you both recognize and understand them.
- Fallacies of ethos relate to credibility. These fallacies may unfairly build up the credibility of the author (or his allies) or unfairly attack the credibility of the author’s opponent (or her allies).
- Fallacies of logos give an unfair advantage to the claims of the speaker or writer or an unfair disadvantage to his opponent’s claims.
- Fallacies of pathos rely excessively upon emotional appeals, attaching positive associations to the author’s argument and negative ones to his opponent’s position.
fallacies that misuse appeals to ethos
Ad hominem: attacking the person making an argument rather than the argument itself.
Example: “Of course that doctor advocates vaccination—he probably owns stock in a pharmaceutical company.”
False authority: relying on claims of expertise when the claimed expert (a) lacks adequate background/credentials in the relevant field, (b) departs in major ways from the consensus in the field, or (c) is biased, e.g., has a financial stake in the outcome.
Example: “Dr. X is an engineer, and he doesn’t believe in global warming.”
Guilt by association/Plain Folk: linking the person making an argument to an unpopular person or group, or linking the person making the argument to ordinary people.
Example: “My opponent is a card-carrying member of the ACLU.”
Example: “Who would you vote for—someone raised in a working-class neighborhood who has the support of Joe the Plumber or some elitist whose daddy sent him to a fancy school?”
Name-calling/Poisoning the well: labeling an opponent with words that have negative connotations in an effort to undermine the opponent’s credibility; undermining an opponent’s credibility before offering that person’s ideas.
Example: “These rabble-rousers are nothing but feminazis.”
Example: “The prosecution is going to bring up a series or so-called experts who are getting a lot of money to testify here today.”
fallacies that misuse appeals to logos
Hasty generalization: jumping to conclusions based upon an unrepresentative sample or insufficient evidence.
Example: “10 of the last 14 National Spelling Bee Champions have been Indian American. Indian Americans must all be great spellers!”
Begging the question: circular argument because the premise is the same as the claim that you are trying to prove.
Example: “This legislation is sinful because it is the wrong thing to do.”
False dilemma: misuse of the either/or argument; presenting only two options when other choices exist
Example: “Either we pass this ordinance or there will be rioting in the streets.”
Post hoc ergo propter hoc/Slippery Slope: Post hoc is a Latin phrase meaning “after this, therefore because of this”; assumes that a first event causes a second event without evidence to show that cause. Slippery slope asserts that one thing will inevitably lead to another without offering adequate support.
Example: “My child was diagnosed with autism after receiving vaccinations. That is proof that vaccines are to blame.”
Example: “We can’t legalize marijuana; if we do, then the next thing you know people will be strung out on heroin.”
Non-sequitur: Latin for “does not follow”; the conclusion is not valid because a premise is untrue (or missing) or because the relationship between premises does not support the deduction stated in the claim.
Example (untrue premise):“If she is a Radford student, she is a member of a sorority. She is a Radford student. Therefore she is a member of a sorority.”
Smoke screen: avoiding the real issue or a tough question by introducing an unrelated topic as a distraction; sometimes called a red herring.
Example: “My opponent says I am weak on crime, but I have been one of the most reliable participants in city council meetings.”
fallacies that misuse appeals to pathos
Appeal to fear, guilt, or pity: using scare tactics to exaggerating possible dangers, evoking an emotional reaction and disregarding the issue at hand.
Example: “Without this additional insurance, you could find yourself broke and homeless.”
Example: “I know I missed assignments, but if you fail me, I will lose my financial aid and have to drop out.”
Appeal to popularity (bandwagon): urging a reader to follow a course of action because “everyone does it.”
Example: “Nine out of ten shoppers have switched to Blindingly-Bright-Smile Toothpaste.”
Appeal to tradition: people have been done it a certain way for a long time; assumes that what has been customary in past is correct and proper.
Example: “We always organize our annual meetings in this way; therefore, we should stick with the same organization for the upcoming year.”
Emotionally Loaded Language: using slanted or biased language
Example: “Only someone out of touch with reality in the 21st century doesn’t do online banking.”
The number and array of logical fallacies can be daunting. The main thing to remember is to look at the way in which an author states and supports the argument in a text. If there are a number of errors in reasoning, the text itself may not be valid for your purposes.
Questions to Analyze the Logic of a Text’s Argument
- Is the claim believable?
- Is the underlying assumption (warrant) acceptable?
- Is the supporting evidence relevant, sufficient, and accurate?
- Has the author cited sources or in some way made it possible for the reader to access evidence used?
- Are there different opinions and perspectives included, especially when there are multiple opinions on an issue?
- Does the author avoid selective use of evidence or other types of manipulation of data?
- Does the offer evidence respectfully, using unbiased language?
- Is there an over-reliance on emotional appeals?
Based on your reading of “Forget Shorter Showers” by Derrick Jensen, answer the following questions intended to help you analyze the argument.
- Identify one logical fallacy in each of the first three paragraphs and in the next-to-last paragraph. You do not have to name the fallacies by their formal names; just identify the errors in reasoning in your own words.
- Identify one overall logical fallacy in the whole argument of this text.