Argument: Claims, Reasons, Evidence | Department of Communication (2024)

Critical thinking means being able to make good arguments. Arguments are claims backed by reasons that are supported by evidence. Argumentation is a social process of two or more people making arguments, responding to one another--not simply restating the same claims and reasons--and modifying or defending their positions accordingly.

Claims are statements about what is true or good or about what should be done or believed. Claims are potentially arguable. "A liberal arts education prepares students best" is a claim, while "I didn't like the book" is not. The rest of the world can't really dispute whether I liked the book or not, but they can argue about the benefits of liberal arts. "I thought the movie was cool" is not an arguable statement, but "the movie was Paul Newman's best" is, for people can disagree and offer support for their different opinions.

Reasons are statements of support for claims, making those claims something more than mere assertions. Reasons are statements in an argument that pass two tests:

Reasons are answers to the hypothetical challenge to your claim:

• “Why do you say that?”
• “What reason can you give me to believe that?” If a claim about liberal arts education is so challenged, a response with a reason could be: “It teaches students to think independently.”

Reasons can be linked to claims with the word because:

• Liberal arts is best [claim] because it teaches students independent thinking [reason];
• That was Newman's best [claim] because it presented the most difficult role [reason];
• Global warming is real [claim] because the most reputable science points in that direction [reason].
• Everyone should stop wearing seat belts [claim] because it would save lives [reason].

If reasons do not make sense in the hypothetical challenge or the 'because' tests, there is probably something wrong with the logic of the argument. Passing those tests, however, does not insure that arguments are sound and compelling.

Evidence serves as support for the reasons offered and helps compel audiences to accept claims. Evidence comes in different sorts, and it tends to vary from one academic field or subject of argument to another. Scientific arguments about global warming require different kinds of evidence than mealtime arguments about Paul Newman's movies. Evidence answers challenges to the reasons given, and it comes in four main types:

Specific instances include examples, case studies, and narratives. Each can be an effective mode of building support for a reason or claim. In a public speech, they offer audiences a way to see an idea illustrated in a particular case. To be effective, specific instances need to be representative of the broader trend or idea they are supporting. With an example as evidence, someone arguing against seat belt use might say "Last year my cousin crashed her car off a bridge and would have drowned if she were wearing her seatbelt" as evidence (the answer to "Why do you believe that?" question.) An opponent might challenge whether this example was a representative one: surely there are many more car crashes that do not end in water, so this one instance is not a fair gauge of the relative safety of not wearing seat belts.

Statistics include raw numbers (117 million visitors to the Rock and Roll Hall of Fame,), averages ('women's bowling teams drink on average two pitchers less then men's'), statistical probabilities ('crossing North Main during rush hour increases your chances of death 20%'), and statistical trends ('applications have risen 40% over the past three years'). In public speeches, statistics have the advantage of seeming objective, authoritative, and factual, but critical audiences will want to know about the sources and methods for determining your statistical evidence.

Testimony, or appeals to authority, come in two main types, eyewitness and expert. Eyewitness or first-hand testimonies are reports from people who directly experience some phenomenon. If a speaker is arguing about toxic waste dumps, a quotation from someone living next to a dump would fall into this category. First-hand testimony can help give the audience a sense of being there. Experts may also rely on direct experience, but their testimony is also backed by more formal knowledge, methods, and training. Supplementing the neighbor's account with testimony from an environmental scientist, who specializes in toxic waste sites, is an appeal to expertise. When using testimony in arguments, you should always make sure the authority you are appealing to is in fact qualified to speak on the topic being discussed.