Evidence is a term commonly used to describe the supporting material in persuasive writing. Evidence gives an objective foundation to your arguments, and makes your writing more than a mere collection of personal opinions or prejudices. Evidence includes:

  • facts and figures
  • examples
  • narratives
  • testimony
  • definition

All are used to convince readers to accept the arguments and recommendations the writer is presenting.

Because you are asking your readers to take a risk when you attempt to persuade them, audiences will demand support for your assertions. Search for evidence that is relevant and timely and that comes from sources your audience will respect and accept.

A few notes about evidence

  • Have more facts and figures than you think you will need.
  • Have the latest facts and figures—make sure your data is up to the minute.
  • Emphasize factual examples.
  • When appropriate, use powerful examples.
  • Use narratives to create identification—to draw your audience into your subject and reinforce their stake in the outcome.
  • Emphasize expert testimony. It carries more weight than prestige or lay testimony. Be prepared to document the qualifications of the experts you use, if they are unfamiliar to your audience.
  • Use multiple sources of evidence.

Proofs are interpretations drawn from evidence that provide readers with good reasons for changing an attitude or following a course of conduct or action. Good reasons are concerned with showing an audience that something is admirable, desirable, or obligatory.

Most importantly, audiences evaluate good reasons in terms of their:

  • Relevance (do they really apply to the situation or issue at hand?);
  • Consequences (what will be the result of accepting or rejecting them?); and
  • Consistency (do they fit together, and do they fit with our other prior beliefs/policies?).

Proofs that produce good reasons have been studied since the time of Aristotle. He suggested in his book The Rhetoric, written in the fourth century B.C., that there are three types of proof:

  • Logos—proof that emphasizes rational evidence;
  • Pathos—proof based on motives and emotions; and
  • Ethos—proof based on the personality, character, and reputation of the writer.

More recent scholars have added one other form of proof:

  • Mythos—proof based on the traditions, identity, and values of a group. The mythos of an organization can be an important element in persuasive business writing.

In most ethical and effective persuasive efforts, particularly in a business setting, logos usually predominates. Ethos and pathos can be important supporting players; pathos is the least used in business.


Let's take a brief look at how proof is structured—in this case, using logical evidence.


  1. A statement is made that must be proven: "Calcium and iron deficiencies are the two biggest nutritional problems for women."
  1. Evidence is presented that supports the statement:
    "Seven out of ten women in America do not get sufficient calcium."
    ". . . study conducted at blah blah medical center showed. . ."
    ". . . pregnant and lactating women consume under minimum daily requirement . . ."
  • Bridge: The general principle which authorizes making the step between the evidence and the claim: "Taking calcium supplements will provide women the necessary calcium and iron their diets do not provide."

  • Foundation: Statement or evidence supporting the bridge if audience won't readily accept the bridge: (cite some evidence showing the efficacy of taking vitamin supplements)
  • .
  1. A claim is drawn from the statement and evidence: "Therefore, women should take ‘CALTRATE with Iron.’" (This is your point of persuasion.)

  2. Additional evidence is provided to support the claim or conclusion:
    "Each tablet contains 600 mg. of calcium bicarbonate."
    ". . . Studies cited in the JAMA, January 1994 issue, report that . . ."
    ". . . A survey of obstetricians (source) conducted by the NIH . . ."

  3. Address any Counterclaims ("Other studies have shown that calcium taken in supplements are not readily absorbed.") with a rebuttal: "Despite arguments presented by some physicians claiming that supplements are not readily absorbed, a recent study at Strong Memorial Hospital in Rochester, NY, showed that calcium supplements can, over time, raise the bone density in women between the ages of 50 and 85."

  4. Qualifiers are provided if needed to indicate the strength of the conclusion or conditions under which it may not apply: "Unless your diet is already rich in calcium and iron, you should start taking CALTRATE Plus Iron." (Use words like probably, unless, with the exception of . . ., etc.)

    Another way of describing this logical proof was designed by Stephen Toulmin. (Stephen Toulmin.The Uses of Argument. Cambridge: Cambridge University Press, 1958.) His design is now the most common deductive model.


    In everyday life, the first part of the argument to emerge is frequently the claim we wish to make.

      Statement/Premise: "Better communication will improve our recruiting record."

    When the reader is already on our side, all we have to do is state the claim. But when the reader resists the claim, we must support it with evidence.

      Evidence: "We are losing recruits to other schools." (data, data, data)

    Just providing evidence may not be enough in difficult situations. The reader has to make a leap of generalization to see the relationship between the evidence and the claim. If the reader doesn't see the relationship—doesn't know it, agree with it, or happen to think of it at the moment—he or she won't be convinced. Adding more evidence won't help. Instead, we need to spell out the general principle or bridge, which authorizes making the step between the evidence and the claim.

      Bridge: "Recruits are more likely to choose schools which communicate with them often during the recruiting process."

    Perhaps the audience won't believe the bridge statement. They might say, "Recruits go to the most prestigious school they can." If the audience might disagree with the bridge, we need to provide it. When the proof is made explicit, the statement supporting the bridge is called the foundation.

      Foundation: "Research shows that frequency and quality of communication were key factors in influencing recruits to attend a specific school. Communication strengthened recruits' initial interest and helped overcome objections. Our informal surveys of recruits show that they receive more mail and phone calls from other schools than from us." (Provide concrete data.)

      Claim/Point of Persuasion: "We should contact all potential recruits by telephone and follow up in writing."

    Sometimes the reader may accept the bridge but think of a counterclaim that negates the claim.

      Counterclaim: "Our communication style might be poor. Frequent communication might hurt rather than help."

    If a counter argument exists, we must provide a rebuttal to it to be convincing.

      Rebuttal: "We will offer training sessions to our coaches and hire a consultant to help them write effective letters."

    Many claims cannot be made with 100% certainty. If the claim is only probably and not necessarily true, we need to limit it.

      Limiter: "Better communication will help us recruit more effectively."

    You can also limit a claim with the words probably and may be able with explicit disclaimers: "These results are accurate with ±5.6 percent." "This projection is based on surveys taken October 28th."


    The following example (A Problem-solving Persuasive Memo) illustrates the use of the Toulmin model in a problem-solving persuasive message. The memo is written to persuade employees not to make personal calls on office phones. The memo makes use of words, phrases, sentences, or paragraphs which:

    1. Build a common ground;
    2. Offer evidence of the problem;
    3. Provide that the problem hurts the organization;
    4. Rebut counterclaims;
    5. Present the solution to the problem in general terms;
    6. Present the complete solution in specific terms;
    7. Picture the problem being solved;
    8. Limit the claims about additional reader benefits that may arise from the solution but are not certain to occur;
    9. Tell readers exactly what to do; and
    10. Build an image of the writer/speaker as someone who's on the same side as readers, helping them to solve their problems and achieve their goals.


    February 19, 200X

    To: All Sales Representatives

    From: James Christopher Smith

    Subject: Improving Service of Customers' Phone Orders

    All of you have told me that your customers are experiencing difficulties in placing orders because all the phone lines are tied up, and that some customers are ordering from other wholesalers as a result. This is causing you a loss in sales commissions.

    The recent opening of the Johnson Wholesale House in Decatur has made competition in our field of wholesale drugs even keener. With the addition of this new warehouse, Johnson can service customers in all our sales areas almost as quickly as we can, and for approximately the same price. This new availability makes it even easier for our customers to call Johnson's instead of us. In fact, Glenn and Jack report that Walgreen's has increased its business with Johnson's from a sixth to a third of its total drug business. Sue and Jerry also say that several of the small independent drug stores in central Illinois, such as the ones in Effingham and Tuscola, have switched to Johnson's from us. With competition as fierce as this, we must make ordering from us a quick and easy operation.

    Most orders are phoned in between 9:30 and 11:30 in the morning and 1:00 and 2:00 in the afternoon, according to the times indicated on the order forms from last month. The phone operators, however, report that the lines are tied up throughout the day, usually by calls from the sales department. In order to relieve congestion, it is necessary to reduce phone activity in the sales department.

    Using the pay phones for personal calls during the peak ordering hours can make more phone lines available to our customers. If possible, calls on company business should be made during non-peak hours. This will enable us to keep more lines open during the peak ordering hours without spending money on costly new lines.

    With the lines open to incoming calls, customers will find that they can place their orders quickly and easily. This will encourage them to keep calling us instead of our competitors, which can mean greater sales for you. In addition, good service helps build good will which may enable you to get a bigger share of your customers' business. The easy phone ordering service will also serve you as an additional selling point for new customers.

    To improve customer relations and realize greater sales, use the pay phones for personal calls between the peak hours of 9:30 - 11:30 and 1:00 - 2:00, and make outgoing business calls during non-peak hours.


    By comparing an argument to the Toulmin model, you can see what kind of statements you need to make an argument convincing. Each of the examples is unconvincing, but the solutions differ.

    Argument 1 "By using XTROCUT tubing, you can cut production time and reduce scrap loss."
    Problem with argument This argument needs evidence to support each to its claims.
    Revised argument "Because XTROCUT comes in lengths and shapes you use most often, you spend less time cutting down longer tubes. Since you can order just the length you want, you won't waste feet every time you need a 10-foot tube."

    Argument 2 "The workers I talked to were split 50/50. The workers at our plant don't agree whether the benefits package is adequate."
    Problem with argument No bridge shows that the "workers I talked to" were a representative sample. The audience may also wonder whether things have changed since the date of the poll.
    Revised argument "I talked to a representative sample of workers. They were split 50/50. Last week, the workers didn't agree whether the benefits package is adequate."

    Argument 3 "Our national advertising campaign will run during the most popular TV shows this month. This ad campaign will increase our sales dramatically."
    Problem with argument Such a claim cannot be made with certainty; too many variables affect sales.
    Revised argument "Our national advertising campaign will run during the most popular TV shows this month. This ad campaign will support our sales reps' efforts to increase sales 5% over last month."