Critical thinking is a process of testing an argument or observation for validity. By breaking a concept down into a series of premises and conclusions, you examine the causal relationship between elements of the observable world and aspects of reality you may not yet have considered. Thinking critically and examining beliefs is a basic survival skill. Without the ability to observe, question, learn and draw sensible conclusions about the world around them, the ancestors of modern humans may never have survived.
Identification of the Argument
Before you evaluate the soundness of an argument, you must first break it apart into its individual components. Identify the argument's premises and conclusion. The premises are statements of known or assumed facts which should not contradict each other. The conclusion is essentially a summation of the premises, or an inference drawn from them. For example, one premise may be that there are seven mice before you. Another premise may be that the seven creatures you see all have tails. These two statements seem to imply the conclusion that all mice have tails.
Once you identify the premises, you can begin to examine each of them for validity. Look for ambiguity or vagueness within the propositions. In the case of the seven mice, the premises reflect an observable reality, so there is no need to question their validity. If a premise stated that the mouse tails before you were made of stored cheese, it would require some additional examination. It would also change the nature of the conclusion. However, since no unusual statements have been made, simply determine whether or not the implications are logical and whether or not they contain any contradictory data.
Deductive and Inductive Reasoning
Once you have examined the premises, move on to the conclusion. Is it supported by the premises? In a deductive argument, the conclusion must be true if its premises are true. You may have seen a mouse without a tail before, or you may simply be able to envision a possible accident or genetic anomaly which results in a tailless mouse, so you judge that the conclusion could be false. When the conclusion's truth value is ambiguous despite the truth of its preceding premises, the argument is known as an inductive argument.
Determine whether or not the argument is sound. Reexamine the argument for poor logic, false premises, omissions or assumptions. In the case of the mouse argument, an assumption is made as to whether or not there are more mice in the world. If there were not, then the traits of the seven mice before you would indeed be those of all mice. However, as long as you can produce additional mice, perhaps even without tails, the argument relies on an assumption. Examine the structure of the argument as well, to determine whether or not it presents a reasoned analysis and a tightly developed line of reasoning.
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