An important part of critical thinking is being able to give reasons, whether it is to support or to criticize a certain idea. To be able to do that, one should know how to identify, analyze, and evaluate argument. 

What is an argument?

In everyday life, people often use “argument” to mean a quarrel between people. But in logic and critical thinking, an argument is a list of statements, Monty Python said: “An argument is a connected series of statements to establish a definite proposition.” There are three stages to an argument: Premises, Inference, and Conclusion. To give an argument is to provide a set of premises as reasons for accepting the conclusion through a gradual inference process.

Stage one: Premises

One or more propositions will be necessary for the argument to continue. They must be stated explicitly. They are called the premises of the argument. They are the evidence (or reasons) for accepting the argument and its conclusions. Premises (or assertions) are often indicated by phrases such as “because”, “since”, “due to” and so on.

The premises of the argument are used to obtain further propositions. This process is known as inferences. In inference, we start with one or more propositions which have been accepted. We then derive a new proposition. The propositions arrived at by inference may then be used in further inference. Inference is often denoted by phrases such as “implies that” or “therefore”.

Finally, we arrive at the conclusion of the argument, another proposition. The conclusion is often stated as the final stage of inference. It is affirmed on the basis the original premises, and the inference from them. Conclusions are often indicated by phrases such as “Therefore”, “It follows that”, “We conclude” and so on.

There are two traditional types of argument, deductive and inductive.

A deductive argument provides conclusive proof of its conclusions. If the premises are true, the conclusion must also be true. A deductive argument is either valid or invalid.

Here is an example of a deductive argument:

Every event has a cause (premise). The universe has a beginning (premise). All beginnings involve an event (premise). This implies that the beginning of the universe involved an event (inference). Therefore, the universe has a cause (inference and conclusion).

An inductive argument is one in which the premises are supposed to support the conclusion in such a way that if the premises are true, it is improbable that the conclusion would be false. Thus, the conclusion follows probably from the premises and inferences.

Here is an example of an inductive argument:

The last ten times I’ve played poker, I’ve won money (premise). I’m playing poker tonight (premise). I’ll win money tonight (conclusion).

In this example, even if both premises are true, it is still possible for the conclusion to be false (maybe I’ll lose money tonight, for example). Words which tend to mark an argument as inductive – and hence probabilistic rather than necessary – include “probably”, “likely”, “possibly” and “reasonably”.

It may seem that inductive arguments are weaker than deductive arguments because there must always remain the possibility of their arriving at false conclusions, but that is not entirely true. With deductive arguments, our conclusions are already contained, even if implicitly, in our premises. This means that we don’t arrive at new information. Inductive arguments, on the other hand, do provide us with new ideas and thus may expand our knowledge about the world in a way that is impossible for deductive arguments to achieve. Thus, while deductive arguments may be used mot often with mathematics, most other fields of research make extensive use of inductive arguments.

References:

1.       http://www.virtualschool.edu/mon/SocialConstruction/Logic.html

2.       http://atheism.about.com/od/criticalthinking/a/deductivearg.htm

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