There are three types of rhetorical appeals, or persuasive strategies, used in arguments to support claims and respond to opposing arguments. A good argument will generally use a combination of all three appeals to make its case.

Logos

Logos or the appeal to reason relies on logic or reason. Logos often depends on the use of inductive or deductive reasoning.

Inductive reasoning takes a specific representative case or facts and then draws generalizations or conclusions from them. Inductive reasoning must be based on a sufficient amount of reliable evidence. In other words, the facts you draw on must fairly represent the larger situation or population. Example:

In this example the specific case of fair trade agreements with coffee producers is being used as the starting point for the claim. Because these agreements have worked the author concludes that it could work for other farmers as well.

Deductive reasoning begins with a generalization and then applies it to a specific case. The generalization you start with must have been based on a sufficient amount of reliable evidence.Example:

In this example the author starts with a large claim, that genetically modified seeds have been problematic everywhere, and from this draws the more localized or specific conclusion that Mexico will be affected in the same way.

Avoid Logical Fallacies

These are some common errors in reasoning that will undermine the logic of your argument. Also, watch out for these slips in other people's arguments.

Slippery slope: This is a conclusion based on the premise that if A happens, then eventually through a series of small steps, through B, C,..., X, Y, Z will happen, too, basically equating A and Z. So, if we don't want Z to occur A must not be allowed to occur either. Example:

In this example the author is equating banning Hummers with banning all cars, which is not the same thing.

Hasty Generalization: This is a conclusion based on insufficient or biased evidence. In other words, you are rushing to a conclusion before you have all the relevant facts. Example:

In this example the author is basing their evaluation of the entire course on only one class, and on the first day which is notoriously boring and full of housekeeping tasks for most courses. To make a fair and reasonable evaluation the author must attend several classes, and possibly even examine the textbook, talk to the professor, or talk to others who have previously finished the course in order to have sufficient evidence to base a conclusion on.

Post hoc ergo propter hoc: This is a conclusion that assumes that if 'A' occurred after 'B' then 'B' must have caused 'A.' Example:

In this example the author assumes that if one event chronologically follows another the first event must have caused the second. But the illness could have been caused by the burrito the night before, a flu bug that had been working on the body for days, or a chemical spill across campus. There is no reason, without more evidence, to assume the water caused the person to be sick.

Genetic Fallacy: A conclusion is based on an argument that the origins of a person, idea, institute, or theory determine its character, nature, or worth. Example:

In this example the author is equating the character of a car with the character of the people who built the car.

Begging the Claim: The conclusion that the writer should prove is validated within the claim. Example:

Arguing that coal pollutes the earth and thus should be banned would be logical. But the very conclusion that should be proved, that coal causes enough pollution to warrant banning its use, is already assumed in the claim by referring to it as "filthy and polluting."

Circular Argument: This restates the argument rather than actually proving it. Example:

In this example the conclusion that Bush is a "good communicator" and the evidence used to prove it "he speaks effectively" are basically the same idea. Specific evidence such as using everyday language, breaking down complex problems, or illustrating his points with humorous stories would be needed to prove either half of the sentence.

Either/or: This is a conclusion that oversimplifies the argument by reducing it to only two sides or choices. Example:

In this example where two choices are presented as the only options, yet the author ignores a range of choices in between such as developing cleaner technology, car sharing systems for necessities and emergencies, or better community planning to discourage daily driving.

Ad hominem: This is an attack on the character of a person rather than their opinions or arguments. Example:

In this example the author doesn't even name particular strategies Green Peace has suggested, much less evaluate those strategies on their merits. Instead, the author attacks the characters of the individuals in the group.

Ad populum: This is an emotional appeal that speaks to positive (such as patriotism, religion, democracy) or negative (such as terrorism or fascism) concepts rather than the real issue at hand. Example:

In this example the author equates being a "true American," a concept that people want to be associated with, particularly in a time of war, with allowing people to buy any vehicle they want even though there is no inherent connection between the two.

Red Herring: This is a diversionary tactic that avoids the key issues, often by avoiding opposing arguments rather than addressing them. Example:

In this example the author switches the discussion away from the safety of the food and talks instead about an economic issue, the livelihood of those catching fish. While one issue may affect the other, it does not mean we should ignore possible safety issues because of possible economic consequences to a few individuals.

Ethos

Ethos or the ethical appeal is based on the character, credibility, or reliability of the writer. There are many ways to establish good character and credibility as an author:

• Use only credible, reliable sources to build your argument and cite those sources properly.
• Respect the reader by stating the opposing position accurately.
• Establish common ground with your audience. Most of the time, this can be done by acknowledging values and beliefs shared by those on both sides of the argument.
• If appropriate for the assignment, disclose why you are interested in this topic or what personal experiences you have had with the topic.
• Organize your argument in a logical, easy to follow manner. You can use the Toulmin method of logic or a simple pattern such as chronological order, most general to most detailed example, earliest to most recent example, etc.
• Proofread the argument. Too many careless grammar mistakes cast doubt on your character as a writer.

Pathos

Pathos, or emotional appeal, appeals to an audience's needs, values, and emotional sensibilities. Pathos can also be understood as an appeal to audience's disposition to a topic, evidence, or argument (especially appropriate to academic discourse). 

Argument emphasizes reason, but used properly there is often a place for emotion as well. Emotional appeals can use sources such as interviews and individual stories to paint a more legitimate and moving picture of reality or illuminate the truth. For example, telling the story of a single child who has been abused may make for a more persuasive argument than simply the number of children abused each year because it would give a human face to the numbers. Academic arguments in particular ​benefit from understanding pathos as appealing to an audience's academic disposition.

Only use an emotional appeal if it truly supports the claim you are making, not as a way to distract from the real issues of debate. An argument should never use emotion to misrepresent the topic or frighten people.