12. What are the three characteristics of valid reasoning?

Reasoning: Arguing Cogently

By David Roberts

(printable version here)

Academic writing requires writers to make claims and support them using evidence of one kind or another. When writers employ good reasoning, it is called "cogent." As you will see, cogency refers to very specific traits of arguments. Discussed in detail below are the three specific characteristics of good arguments.

Three Characteristics of Good Arguments

A cogent argument has three characteristics, according to Kahane and Cavender (1998):

1. All its premises are true. The premise (s), the reasons for accepting the conclusion (s), must be true - or, at least, believable - in order for the argument to be cogent. 2. It considers all relevant information. Good arguments also consider all information likely to be relevant. This consideration includes addressing counter-arguments and objections to both the premises and the conclusion. 3. It is logically valid. Validity, defined very loosely, means that the premises do, in fact, give readers reason to accept the conclusion the writer puts forth.

A Good Argument and a Bad Argument

Consider the following two arguments. The first argument displays good reasoning and the second demonstrates fallacious reasoning.

1. If it is raining, then the ground is wet.

2. It is raining.

3. Therefore, the ground is wet.

The first premise specifies a conditional relationship. This relationship is denoted by the if/then structure of the sentence. If A happens, then B happens too. This structure is called the major premise of the argument. The second, minor premise of the argument tells us that the "if" part of the first premise takes place. The third statement, the conclusion, then asserts that the "then" part of the first statement takes place as well. This argument form is known as modus ponens.

Now, consider a second argument.

1. If it is raining, then the ground is wet.

2. The ground is wet.

3. Therefore, it is raining.

At first glance, one may be tempted to believe that this argument shows good reasoning as well. Since we have already established the truth-value of the first premise, and since we will assume that somewhere the ground is, in fact, wet, let us consider the relationship between the premises and the conclusion. This argument is invalid: the truth of the premises does not give us grounds to accept the conclusion as true. There are reasons other than rain that the ground could be wet: the sprinkler system could be on, for instance.

Falsely inferring that it is raining because the ground is wet is known as affirming the consequent. This fallacy and others are discussed in greater detail in our logical flaw sections: general inferential errors, errors in causality, errors in generalization, and other fallacies.

The First Characteristic: True Premises

This first condition for a cogent argument is the one likely to involve the most research. An important decision writers must make in their papers is when to take a premise as accepted or whether it needs support from outside research. Judgment in this regard is often formed with experience writing and familiarity with the topic. In any case, many premises will have to be supported in some fashion. See our page on strategies for reasoning and avoiding fallacies for more advice on this topic.