Chapter 20: Logical Reasoning

Learning Objectives

After reading this chapter, the student will be able to:

  1. Define critical thinking, deductive reasoning, and inductive reasoning.
  2. Distinguish between inductive reasoning and deductive reasoning.
  3. Know the four types of inductive reasoning.
  4. Know the common logical fallacies.
  5. Become a more critical listener to public speeches and more critical reader of source material.

What is Good Reasoning?

In Chapter 13, we reviewed ancient and modern research on how to create a persuasive presentation. We learned that persuasion does not just depend on one mode, but on the speaker using his or her personal credibility and credentials; understanding what important beliefs, attitudes, values, and needs of the audience connect with the persuasive purpose; and drawing on fresh evidence that the audience has not heard before. In addition to fresh evidence, the audience expects a logical speech and to hear arguments that they understand and to which they can relate. These are historically known as ethos, pathos, and logos. This chapter will deal with the second part of logos, logical argument and using critical thinking to fashion and evaluate persuasive appeals.

We have seen that logos involves composing a speech that is structured in a logical and easy-to-follow way; it also involves using correct logical reasoning and consequently avoiding fallacious reasoning, or logical fallacies.

Although it is not a perfect or literal analogy, we can think of correct reasoning like building a house. To build a house, you need materials (premises and facts) a blueprint (logical method), and knowledge of building trades (critical thinking ability). If you put a person out in a field with drywall, nails, wiring, fixtures, pipes, and wood and handed him a blueprint, he would need knowledge of construction principles, plumbing, and reading plans (and some helpers), or no building is going up. Logic could also be considered like cooking. You need ingredients, a recipe, and knowledge about cooking. In both cases, your ingredients or materials must be good quality (your information and facts must be true); your recipe or directions must be right (the logical process); and the user must know what he or she is doing.

In the previous paragraph, analogical reasoning was used. As we will see in Section 14.2, analogical reasoning involves drawing conclusions about an object or phenomenon based on its similarities to something else. Technically, it was a figurative analogy, not a literal one, because the two processes are not essentially the same. A figurative analogy is like a poetic one: “My love is like a red, red rose,” (Robert Burns, 1759-1796); love, or a loved person, and a flower are not essentially the same. An example of a literal analogy would be one between this college, Dalton State, and another state college in Georgia with a similar mission and similar student bodies.

Analogical reasoning is one of several types of logical reasoning methods which can serve us well if used correctly, but it can be confusing and even unethical if used incorrectly. In this chapter we will look first at “good” reasoning and then at several of the standard mistakes in reasoning, called logical fallacies. In higher education today, teaching and learning critical thinking skills are a priority, and those skills are one of the characteristics that employers are looking for in applicants (Adams, 2014). The difficult part of this equation is that critical thinking skills mean slightly different things for different people.

Involved in critical thinking are problem-solving and decision-making, the ability to evaluate and critique based on theory and the “knowledge base” (what is known in a particular field), skill in self-reflection, recognition of personal and societal biases, and the ability to use logic and avoid logical fallacies. On the website Critical Thinking Community, in an article entitled “Our Concept and Definition of Critical Thinking” (2013), the term is defined this way:

Critical thinking is that mode of thinking — about any subject, content, or problem — in which the thinker improves the quality of his or her thinking by skillfully analyzing, assessing, and reconstructing it. Critical thinking is self-directed, self-disciplined, self-monitored, and self-corrective thinking. It presupposes assent to rigorous standards of excellence and mindful command of their use. It entails effective communication and problem-solving abilities, as well as a commitment to overcome our native egocentrism and sociocentrism.

Critical thinking is a term with a wide range of meaning, one of which is the traditional ability to use formal logic. To do so, you must first understand the two types of reasoning: inductive and deductive.

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