PHI-130: Critical Reasoning/Module 4/Lecture

In order to evaluate arguments successfully, let us consider the following useful steps in argument evaluation:

Step 1: Understand the meaning of the argument.

Step 2: Identify the conclusion of the argument.

Step 3: Locate the reasons that support the conclusion of the argument.

Step 4: Determine whether the reasons offered in support of the conclusion are acceptable.

Step 5: State your own opinion on the issue that is debated. Here we have to decide whether the argument that is presented is a good argument, or not, and to provide reasons why we say so.

It is helpful to look out for definitions used in arguments. Sometimes people use definitions of the key concepts in their arguments in an attempt to clarify the concepts and to prevent misunderstanding in communication. For instance, in an argument in favor of active voluntary euthanasia, an arguer would define this key concept in order to distinguish it from other forms of euthanasia. Obviously, the strength of her argument would depend on the accuracy of her definition of active voluntary euthanasia.

When we have to decide whether an argument is good or bad, it is useful to look out for definitions arguers use in their arguments and determine whether the definitions are successful. It might be useful to explore the use of definitions in your online references: look for references to definitions, counterexamples and counterarguments. However, you need not memorise these definitions. It will suffice just to know that it is important to define or explain the meaning of the concepts used in arguments, whether we evaluate or construct arguments. The reason for this, as we have already said, is that often the acceptability of an argument depends on how the concepts used in it are explained.

Although there are no definite criteria to evaluate arguments, there are some guidelines we can use to distinguish between good and bad arguments. Here are some possible guidelines:

• A good argument is a sound argument.
• A good argument is an argument that is consistent.
• A good argument provides sufficient and relevant reasons to support its conclusion.
• A good argument supplies evidence or reasons that are compatible with other claims we know are true.

Please review your online references for examples and explanations related to distinguishing between good and bad arguments, as well as recommended steps in argument evaluation.

Types of Arguments

When we think of structures in general, we think of a combination of parts that belong together, for instance, a bridge, a building, a sentence, et cetera. In order to evaluate the structure, you need to know the requirements for that particular type of structure. The same applies to the evaluation of arguments.

The evaluation of arguments requires an understanding of the type of argument being evaluated and of the criteria for soundness which are appropriate to arguments of that type. When we analyze and evaluate arguments, we should be able to recognise which type of argument we are dealing with. This is because different analyses and evaluative approaches are required, depending on the type of argument we are dealing with. In this section I will introduce you to four types of arguments: empirical, value, deductive and inductive arguments. Together we will explore the difference between these types of arguments.

Deductive vs. Inductive Arguments

In a deductive argument the premises already contain the conclusion. If all the premises in a deductive argument are true (in a provable sense), then its conclusion must be true also, because the claim asserted by its conclusion has already been stated in its premises. Put differently, in a valid deductive argument the truth of the premises supports with certainty the truth of the conclusion. Unlike deductive arguments, inductive arguments have conclusions that supply more information than is contained in their premises. In an inductive argument the supporting connection between its premises and conclusion is loose and there is no strict proof in induction. We can thus say that inductive reasoning is a matter of reasonable expectation based on experience, such as observation. Inductive arguments are common in everyday situations and in the domain of science in its search for knowledge.

An example of a deductive argument is the following:

If Susan is a mother, then Susan is female.

Susan is a mother.

Therefore, Susan is female.

Here is an example of an inductive argument:

The phenomenon of consciousness cannot be explained according to Descartes’ dualistic view of mind and body.

Consciousness is not located in the mind, or the body.

Therefore, consciousness is a field of experience “situated” in the world.

Note: The conclusion of this argument infers information beyond the contents of the premises. In a valid deductive argument the structure of the argument is valid and the premises give sufficient support for the conclusion to follow. For example:

All human beings are mortal.

George is a human being.

Therefore, George is mortal.

This is a valid deductive argument because its structure is valid and the premises provide sufficient support for the conclusion to follow logically.

We can present the structure of the argument as follows:

[All human beings are mortal] 1

[George is a human being] 2

Therefore,

[George is mortal] 3

Conclusion: 3

Premises: 1, 2

The structure of this argument is valid. Do you still remember how we establish whether the structure of an argument is valid or not? If you have forgotten, go back to the sections that explore “Valid deductive arguments” and “Invalid deductive arguments” in your online references.

The argument in our example is valid because its structure is valid and the premises give sufficient support for the conclusion to follow logically. Whether the argument is sound, that is, acceptable, is another matter, as we will see when we explain the difference between the validity and soundness of arguments in number 4 below.

An invalid deductive argument is an argument in which the structure is invalid and the premises fail to give sufficient support to the conclusion. For example:

If Philippa is fit, she will run the marathon.

Philippa is not fit.

Therefore, she will not run the marathon.

The structure of the argument is presented as follows:

[If Philippa is fit, she will run the marathon.] 1

[Philippa is not fit.] 2

Therefore,

[she will not run the marathon.] 3

Conclusion: 3

Premises: 1, 2

The structure of the argument is invalid.

Apart from the fact that the structure of the above argument is invalid, the premises of the argument do not give sufficient support for the conclusion to follow. There might be many reasons why Philippa will not run the marathon: the fact that she is not fit is simply one such reason. Alternatively, she might decide to run the marathon even though she is not optimally fit.

Consult your online references to find out more about the differences between the three major types of inductive arguments: statistical extrapolations; inductive reasoning by analogy; and cause-and-effect reasoning.

When we evaluate arguments we should remember that there are different types of inductive arguments, because we evaluate different arguments differently.

The validity of arguments refers solely to their structure (form) and not their content. When we establish the validity of an argument, we look at the relationship between the premises and the conclusion of the argument. The soundness of arguments refers to the contents of their premises and conclusion. When we assess the soundness, or acceptability, of an argument we want to establish whether or not the evidence provided by the premises is actually true, or acceptable. Let us give an example to explain the difference between the validity and the soundness of arguments:

All creatures on the planet Mercury have pointed ears.

Beauty is a creature on the planet Mercury.

Therefore, Beauty has pointed ears.

We can present the structure of the argument as follows:

[All creatures on the planet Mercury have pointed ears]1.

[Beauty is a creature on the planet Mercury]2.

Therefore,

[Beauty has pointed ears]3.

Conclusion: 3

Premises: 1, 2

The argument is valid because its structure is valid. Also, the conclusion follows logically from the premises. But the argument itself is clearly absurd and senseless. The argument is unsound because, when we evaluate the premises of the argument, it is clear that the premises do not give adequate evidence for the conclusion to be true.

Summary

In this Learning Pathway we have explained some important aspects of argument evaluation. We have explored the difference between various types of arguments and we have noted that the evaluation of arguments requires an understanding of the type of argument being evaluated. We have seen that the reason for this is that different analyses and evaluative approaches are required, depending on the type of argument we are dealing with. In the next section you will have the opportunity to evaluate arguments on your own.