Reason and Logic - The Building Blocks of a Persuasive Argument

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A persuasive argument is built from the ground up. Approach it the same way you would approach the planning and construction of a home. It must have a solid foundation, reinforced with facts and logic, before the ornamental fiddly bits (humor, style and delivery) are added.

Building The Foundation

The first step is to build the foundation of your argument, using reason and logic to state your case convincingly and successfully. Make your points, and raise and answer possible doubts as you go along. This helps establish your credibility.

You can use reasoning to construct your foundation and the framework of your case in several different ways, each of which can be very effective:

• Build your argument by reasoning from the specific to the general; using strong, relevant individual points to prove a broader case.
• Or take the opposite approach, using a strong general truth to arrive at a smaller, more specialized conclusion, reasoning from the general to the specific.
• Reason by analogy, using powerful symbols or parallels to lend credibility to your case.
• Use the cause and effect argument, establishing a logical connection between certain factors and actions and certain results, either as a case for changing the results by changing the causes, or supporting the interaction of cause and effect for its positive results.
• Or connect factual symptoms or clues to explain a situation or recommend a remedy.

Each method works - but only when you choose the right facts and make the right logical fit between the evidence you’ve assembled and the conclusion you want your audience to reach.

Argument and Evidence

An argument is a group of reasons leading to a conclusion. Evidence, together with the conclusion that the evidence supports, equal an argument. The process of reasoning allows us to form conclusions on the basis of the evidence. Scientific research, forensics, technical innovation, logic, mathematical theory, philosophy - all have their origins in this process.

When presenting an argument in a speech, you attempt to prove to your listeners that what you say is true or practical or worth pursuing. In many cases it may be difficult to prove your conclusion in any objective sense. However, as a speaker, your objective is to establish the probability of your conclusions in the minds of the audience. So the process is partly a logical one of demonstrating that what you say is probably true, and partly a psychological one of persuading your listeners to accept the conclusions you have drawn.

Gathering and Testing Your Evidence

1. Your argument is only as good as your supporting evidence can make it. Therefore, it is important that your information be as recent as possible. In our rapidly changing world, information can change and become obsolete overnight. Make sure that you review and update your support materials regularly.

2. Gather and corroborate your evidence from several different sources and perspectives, but which all point to the same conclusions.

3. Find the most unbiased sources possible to support your conclusion. Remember that no source is completely objective. Therefore when you are evaluating your evidence, ask yourself how the evidence was gathered, what bias each source may have, in what direction the source is trying to lead us, and what vested interest the source may have which would lead them to this conclusion, based on the evidence.

Basing an Argument on Specific Instances and Generalizations

Specific Instances

In reasoning from specific instances, several instances are examined and then a general conclusion is made about all such instances. This form of reasoning is useful when you want to develop a general theory, but cannot examine all situations or instances in which it might apply. This type of reasoning is used by marketers doing random surveys among certain population segments. They can draw general conclusions about the public’s tastes from sampling a percentage of the public and getting their opinions. After drawing your conclusions, you need to test your reasoning:

1. It is important to examine a sufficient number of specific instances to justify your conclusions. But how many instances are enough? Keep in mind the following two guidelines: (a) the larger the group you wish covered by your conclusion, the greater the number of specific instances you should examine; and (b) the greater the diversity of items in the group, the greater the number of specific instances you will have to examine. Stress in your speech that your specific instances are of sufficient number to support your conclusions.

2. Were the specific instances you examined representative of the group as a whole? As an example, if you wanted to illustrate that more people prefer a certain type of carbonated soft drink, you cannot just limit your sampling to teenage boys aged 13 to 16. You must survey people of both sexes in various age groups, income levels, ethnic backgrounds and occupations in order to make your findings representative of the general population. Illustrate for your audience that your specific instances are indeed representative of the whole group and not only of one or two subsets of that group.

3. Are there significant exceptions? When you examine specific instances and attempt to draw a conclusion about the whole, take into consideration any significant exceptions. These exceptions will qualify any conclusion you make, and omitting them from your evidence will hurt your credibility. Careful questioning by an astute audience member will not only show up such omissions but will effectively destroy any trust or confidence your audience has in you.

Generalizations

You may also argue in the other direction, in other words, from a general principle to some specific instance. That is, you begin with some general statement or axiom that is accepted as true by the audience and argue that since something is true of the entire class or category, it must also be true of the specific instance, which is a member of that class or category. If we know that all birds have feathers, and we know that a rooster is a bird, and we are asked to speculate whether Farmer Brown’s rooster has feathers, we can generally infer that the rooster does indeed have feathers. We now need to test our reasoning in this direction:

1. Is the general principle true or at least probably true? Obviously, if the general principle is not true, it would be useless to apply it to any specific instance. In most cases you cannot know if a general principle is true, simply because you cannot examine all instances of the class. Consequently, what we are really dealing with is a general principle that seems to be "probably true most of the time". Thus our conclusions about any specific instance will also only be "probably true". Since we're talking about birds, let's consider the argument that birds can fly. This generalization is true most of the time, but it does not apply to all specific instances as there are numerous birds which CANNOT fly - the kiwi, the ostrich, the emu and the penguin, to name a few.

2. Be certain that the specific instance clearly fits with the general principle. As an example, if we know that all sedans are blue, we can infer that Ms. Jones’ car is blue ONLY if we are sure that it is a sedan. Make sure that your general principle is one that is accepted by your audience. If you're trying to prove the factual existence of zombies, it is likely that no amount of evidence you can provide will succeed in convincing the audience of your conclusion. Unless you're talking about the British rock band. Which does exist. To this day. Believe it.

Reasoning from Analogy

The use of analogy as a reasoning tool takes items that are similar in nature and share a number of common features, then extrapolating that they are probably alike in other ways that have not yet been tested. Literal analogy compares items that are of the same class. If you wanted to determine the advantages or disadvantages of driver’s side air bags in a new model of car, you could examine the safety records of such air bags in Fords, Chryslers, Hondas and Toyotas and then extrapolate that the findings would also apply to your new model.

In a figurative analogy, the items compared are from different classes. These analogies are useful for emphasizing a point, but do not constitute logical proof. For instance, you could borrow from Forrest Gump and compare life to a box of chocolates - “You never know what you’re gonna get.” In testing the adequacy of an analogy, you should ask the following questions:

1. Are the two situations used in the comparison alike in essential respects?
2. Do the differences between the items make a substantial difference to your conclusion?

To use analogy effectively, you must stress the numerous and significant similarities between the items being compared and minimize the differences between them. Enumerate the differences that do exist between the items, but explain to the audience that these differences do not undermine the validity of your argument, and give your reasons for dismissing those differences.

Reasoning from Cause and Effect

Reasoning based on cause and effect can be followed in either direction, i.e. from observed cause to unobserved effect or from observed effect to unobserved cause. The first instance, from observed cause to unobserved effect, is of course much easier to document with real evidence. For instance, we know that obesity can lead to high blood pressure, heart attack, blocked arteries and numerous other health problems. Therefore we can state that the way to reduce these risks is to lose weight.

Reasoning from observed effect to unobserved cause can be more difficult to provide evidence for, as it involves speculation to some extent with respect to the cause(s) responsible for the effect. As an example, let’s say we are investigating the reasons why obesity in children is on the rise. Is it due to overindulgence in junk food, lack of exercise, too much time spent in front of the TV and game console, or are there other causes that we are overlooking which are contributing to this effect? Test your reasoning by asking the following questions:

1. Are there factors other than the factors on which you base your argument which might be producing the observed effects, or which are acting in combination with the postulated factors?
2. When two things occur together, it can be difficult to determine which is the cause and which is the effect. Investigate the causality in both directions to determine which is which, or if, as may be a possibility, both are effects caused by some other factor.
3. Is there evidence for a causal rather than merely a time‑sequel relationship? Two things may vary together, but they may not be related in a cause‑effect relationship. For instance, divorce frequently results after repeated instances of infidelity, but infidelity itself may not be the cause of the divorce. Thus, although infidelity may precede divorce, it may not be the cause of it. Whatever is the cause of the infidelity might then be more reasonably assumed to be the cause of the divorce.

To use reasoning from causal relationships effectively, stress the following points:

• Other causes are not significant and may for all practical purposes be ruled out.
• The causal connection is in the direction postulated, that is, the cause is indeed the cause and the effect the effect, and not vice versa.
• The evidence points to a causal relationship and not merely a time-sequel relationship.

Depending on the impact you want your speech to have, you can make your audience realize that this causal connection can be altered to their advantage. It may be strengthened if the effect is desirable or broken if the effect is undesirable.

Reasoning from Sign

The general procedure for this type of reasoning is simple. If a sign and an event or condition are frequently paired, the presence of the sign is taken as proof of the presence of the event or condition. The best example of this type of reasoning is medical diagnosis, which looks at the manifestation of symptoms to indicate the presence of a disease or illness.

In reasoning from sign, it is necessary to ask the following questions:

1. Do the signs fully support the conclusion drawn? In most cases, you can only be reasonably sure of your conclusion, not absolutely positively 100% sure.
2. Are there other signs that point to the same conclusion? Generally, the more signs that point toward the conclusion, the more confidently you can postulate that your conclusion is valid.
3. Are there contradictory signs, or signs that point toward one or more contradictory conclusions? Be prepared to account for these.

To use this type of reasoning effectively with your audience, stress the certainty of the connection between the signs and the conclusion, and make it clear in what way the signs support the conclusion. Make them see that because these signs are present, no other possible conclusion is likely or reasonable. As with other forms of reasoning, try to answer the anticipated objections of the audience to your line of reasoning.

Be prepared for your audience to question your conclusion if one or more of your indicators are contradictory or point towards a contradictory conclusion – stress the fact that there are other signs which support your conclusion and when taken together with the rest of the indicators, contradictory or not, can only lead to one reasonable conclusion.