23 Arguments and Premises

What is a premise?

In a deductive argument, the premises are the statements whose logical relationship allows for the conclusion. The first premise is checked against the second premise in order to infer a conclusion.

Premise:      All raccoons are omnivores.
Premise:      This animal is a raccoon.
Conclusion: This animal is an omnivore.

Why should I evaluate the truth of a premise?

A formal argument may be set up so that, on its face, it looks logical. However, no matter how well-constructed the argument is, the premises must be true or any inferences based on the premises will be unsound.

Inductive reasoning often stands behind the premises in a deductive argument. That is, a generalization reached through inductive reasoning is the claim in an inductive argument, but a speaker or writer can turn around and use that generalization as a premise in a deductive argument.

Premise (induced): Most Labrador retrievers are friendly.
Premise (deduced): Kimber is a Labrador retriever.
Conclusion: Therefore, Kimber is friendly.

In this case we cannot know for certain that Kimber is a friendly Labrador retriever. The structure of the argument may look logical, but it is based on observations and generalizations rather than indisputable facts.

How do I evaluate the truth of a premise?

One way to test the accuracy of a premise is to determine whether the premise is based upon a sample that is both representative and sufficiently large, and ask yourself whether all relevant factors have been taken into account in the analysis of data that leads to a generalization. Another way to evaluate a premise is to determine whether its source is credible. Are the authors identified? What is their background? Was the premise something you found on an undocumented website? Did you find it in a popular publication or a scholarly one? How complete, how recent, and how relevant were the studies or statistics discussed in the source?

Here it would help to review the following questions from the section of the Handbook that covers the CORE 102 Research Narrative assignment:

The following argument is based upon research published in a peer-reviewed medical journal. The author has an extensive background in public health including a medical degree and doctorate in medicine. He is employed by the Public Health Agency in Barcelona, Spain.


Plans-Rubío, P. (2012). The vaccination coverage required to establish herd immunity against influenza viruses. Preventive Medicine 55, 72-77.

Judging from what we know about credible sources, we can feel confident using the following the following argument in our own research even though it is based upon inductive premises.

Premise (induced):  Against most influenza viruses, an 80-90 % vaccination rate for adults is required for herd immunity (Plans-Rubío, 2012, p. 76).
Premise (induced):  In 2009-2010, the influenza vaccination rate for adults was 42 % (p. 76).
Claim:   In 2009-2010, the influenza vaccination rate among adults was not sufficient for herd immunity.

The source is highly credible in part because it is written by an expert for experts. That fact may make a source a challenging read for ordinary readers. It is a medical study based on sufficient, representative, and relevant data that has been carefully analyzed by someone highly qualified in the field. Depending on the nature of an assignment and whether a course is for majors or non-majors, you may be allowed to use some sources that report on studies rather than the original studies themselves. However, you should consult the primary sources whenever possible.

For more information on the types of sources, review What is a primary source?What is a secondary source?, and What is a tertiary source? under the Opposing Viewpoints assignment in CORE 101.

Why should I evaluate unstated or suppressed premises as well as stated ones?

An unstated or suppressed premise is assumed rather than voiced outright but is nevertheless needed for an argument to work. Consider this highly unscientific poll conducted by a TV news station. “Which do you believe Senator Hillary Clinton is most out of touch with: illegal immigration, border security, or the American people?” The pollster is operating as if it is unquestionable that Clinton is out of touch with something. In other words, the question presupposes that she is “out of touch.” However, this unstated premise is debatable once it is brought out into the open. Is she in fact out of touch at all? This is actually a type of logical fallacy, begging the question, which will be covered in a later section.

A listener or reader who is not alert to such unstated or suppressed premises is, without realizing it, agreeing to debate on the communicator’s terms—when those terms may be unfair. In fact, on more complex or serious issues it is often things people take for granted that may actually deserve the most critical scrutiny. For example, in the argument “This medication is labelled as totally natural, so it is safe for me to take it,” the suppressed premise—that “natural” guarantees “safe”—is not trivial and can certainly be challenged.

How does argument diagramming or outlining help to illuminate the structure of an argument?

Besides recognizing the use of induction and deduction, you can use diagramming or outlining to develop an understanding of an argument’s overall structure. Remember that an argument as defined here isn’t a “quarrel”, but rather a group of statements, some of which, the premises, are offered in support for another, the conclusion. So the first order of business in analyzing an argument is to recognize what the main claim is—the conclusion—and what other claims are being used to support it—the premises, which is much easier to do when the arguer is explicit about the steps in the argument. The arguer can make the steps clear by using premise and conclusion indicator terms as signposts. Below is a list of such terms.

Words that introduce or signal an argument conclusion include therefore, sowe may conclude/inferthus, and consequently. Words that introduce or signal argument premises include it follows thatimplies that, as a resultbecause (non-causal meaning), since, for the reason thatfor, and.*

*and often signals the introduction of a further premise, as in “You should believe Z because reason 1 and reason 2″.

When you are diagramming or outlining an argument, if the “flow” of an argument from premises to conclusion isn’t readily apparent, then remember to use the above indicator terms to help you decide which claim is the conclusion and which claims are the premises. Using the indicator terms is particularly helpful because a conclusion may be stated first, last, or anywhere in between. People do all three when they write or talk in real life, so we cannot tell whether a statement is a conclusion simply by where it is positioned in the argument.

What is the purpose of diagramming or outlining an argument?

Diagramming or mapping someone else’s argument serves a double purpose. First, the process helps you clearly see just what the other person is saying. It helps you identify the logical structure of the argument, which is necessary if you are to assess the strengths and weaknesses of the argument in order to know whether or not to accept it. Second, you develop skills of analysis that you will need in order to organize and present arguments in support of a position that you may want to take on some question or issue.

What are the steps to diagramming or outlining an argument?

Here are the basic moves that are required in order to create a clear diagram or outline of an argument.

Identify all the claims made by the author. Since a sentence can contain multiple claims, rewrite statements so that you have one claim per sentence. Adopt some sort of numbering or labeling system for the claims—your instructor may have one that she wishes you to follow.

Eliminate “fluff.” Ignore repetitions, assurances (assertions not backed by evidence or reasons), and information that is unrelated to the argument.

Identify which statements are premises and which statement is the main conclusion.

Recognize that there may be sub-conclusions in addition to a final or main conclusion. You may think of a sub-conclusion as the end point of a sub-argument nested inside the larger argument. Although the sub-conclusion is itself the conclusion of a nested argument, supported by premises, it also functions as a premise supporting the final or main conclusion.

Recognize that some premises are independent and others linked. If you were drawing or mapping the argument, you would be able to draw an arrow from an independent premise directly to the conclusion it supports. Linked premises, however, are multiple statements that must be combined to provide support for a conclusion. If you were drawing or mapping the argument, you would have to find some way to show that the linked premises as a group support the conclusion. You might use color coding, or underlining, or circling, or + signs—some way to connect the linked premises before drawing one arrow from the clustered premises to the conclusion they support.

How can the argument’s paragraphing help me evaluate how the author uses premises?

An author must organize her material to guide the audience through her argument. One tool available to an author is the paragraph. The sentences clustered together in a paragraph should be tightly connected in terms of content. In the commonest form of paragraph, the clustered sentences collectively develop an idea explicitly stated in a topic sentence and don’t contain any extra material related to other ideas. The paragraphs themselves should be placed in an order that reflects some overall plan so that the paragraphs reveal the steps or stages of the argument.

The premises may be said to be key steps or stages in the argument. A well-constructed argument therefore may use each premise as a topic sentence for a paragraph. Additionally, a premise may serve as the guiding idea for a group of paragraphs, each developing a subtopic. For example, the premise, reached by induction, that “College students overestimate the amount of binge drinking that is taking place” might introduce a cluster of three paragraphs, each showing that the overestimation varies by subgroup—with member of sororities, member of fraternities, and non-Greek populations arriving at different estimates.

Look to see whether the author has used paragraphing-by-premise to organize her argument and outline its structure for the audience. You should also ask yourself whether any paragraphs are missing. That is, as you consider what premises serve as the foundations of the argument, be alert for the suppressed ones, the premises that the author assumes to be automatically true. These unacknowledged premises may be ones that the author hopes the audience will not notice or question. In your analysis call her on it by determining where a paragraph on that premise should have appeared in the argument.

How is a conclusion like a thesis statement?

When we talk about a paper, we usually talk about the paper’s main claim as being its thesis statement. But of course a paper that just makes a claim or states an opinion but offers no supporting reasons or arguments isn’t much of a paper. We would be bothered by reading an editorial in which someone stated a strong opinion on some public issue yet did nothing to justify that opinion.

When an author supports a thesis with reasons, then the thesis statement can be described as the conclusion of an argument, with the supporting reasons being that argument’s premises. The argument now has a structure that can be outlined or diagrammed.


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