Chapter One: Critical Thinking:

…Critical thinking is reflective thinking. The critical thinker thinks (infers, reasons) reflectively. But what does it mean for thinking to be reflective in a way that tends to make it critical? Critical thinking is reflective in that it observes its own progress, evaluates each step to decide whether it is justified, and corrects its own errors. The critical thinker might originally have taken the thunderous sound for the sonic boom of a jet plane advancing beyond the speed of sound. But she ruled this out by the absence of the attending screeching sound of an accelerating jet, and also by being unable to see any plane in the sky. Then she confirmed the sound was thunder by spotting dark, menacing clouds on the horizon with heat lightning as well. Critical thinking is not perfect thinking because critical thinkers do make mistakes. But the self-observing and self-correcting nature of critical thinking means they make fewer mistakes than those who do not think critically.

Critical thinking is sometimes mistaken as negative thinking or destructive thinking. But look at the relation of critical thinking to belief. It is not the goal of critical thinking to destroy belief but to arrive at reasonable belief. Critical thinking is not a negative thinking as opposed to a positive or a creative thinking. The critical thinker does ask questions, but she asks them in order to decide what is reasonable to believe. The critical thinker is obviously not so gullible that she believes everything she is told. But neither is she so skeptical that she believes nothing she is told. The critical thinker distinguishes reliable testimony from unreliable and weighs evidence to decide what is reasonable. …

…Once evidence or reasons are advanced in support of an opinion or belief, the result becomes an argument. The belief or opinion is the conclusion of the argument. The activity of analyzing whether the belief is actually supported by evidence or reasons is called argument analysis, and argument analysis is what this book is organized around. It is here conceived broadly to include recognizing an argument, clarifying it or establishing what is intended to support what, and evaluating it, deciding whether the claimed support is actually there.

Taking the Socratic method as a model critical thinking activity, you first learn to criticize the arguments and claims of others, then make the reflective twist of turning this criticism on your own arguments and claims. In a sense you learn to internalize the critic of your own position, or to ask of it the questions that would be asked by a penetrating critic like Socrates. You take the attitude toward your own position of someone who is considerably more skeptical of its merits than you may be initially.

Chapter Six: Argument Analysis by Diagramming

…A natural question arises concerning the convergent and linked arguments. Since we have already indicated that in some cases it is quite difficult to decide whether the given argument is convergent or linked, how are we to master this skill? There are two quite different responses to this legitimate question.

The first response is that pinning a pattern label on a given argument is not the ultimate goal of argument analysis. That goal is to learn enough about the argument by analysis, diagramming, and evaluation to decide whether it is strong or weak. To put this another way, argument diagramming is not an end in itself but a tool in the service of argument analysis and evaluation. So it is the questions you must ask and attempt to answer that are more important than the decision on convergent or linked itself. For you must ask how each premise relates separately to the conclusion, how each relates to the other relative to the conclusion, and whether this makes their support for the conclusion stronger or weaker. These questions would have to be asked and answered for the purpose of evaluating an argument even if we did no diagramming of arguments. So one purpose of diagramming is to provide an effective way of raising these questions.

The second response is that there is an operation we can perform—suggested by Stephen N. Thomas—to determine whether a given argument is convergent or linked. The operation is the removal of a premise. If the argument is greatly weakened by this, it is linked. If its strength is not affected, it is convergent.

Chapter Seven: Evaluating Arguments