13.4: Reasoning- Making Good Decisions, And Learning from Them

Section Learning Objectives

• Differentiate deductive from inductive reasoning.
• Define heuristics and describe types.
• Outline errors we make when reasoning.

Types of Reasoning

Though you are sitting in a college classroom now, how did you get there? Did you have to choose between two or more universities? Did you have to debate which area to major in? Did you have to decide which classes to take this semester to fit your schedule? Did you have to decide whether you were walking, riding a bike, or taking the bus to school? To answer any of these questions, you engaged in reasoning centered on making a good decision or judgment. There are two types of reasoning we will briefly discuss — formal or deductive and informal or inductive.

First, we use formal or deductive reasoning when the procedure needed to draw a conclusion is clear and only one answer is possible. This approach makes use of algorithms or a logical sequence of steps that always produces a correct solution to the problem. For instance, solve the following problem:

3x + 20 = 41

• Step 1 — Subtract 20 from both sides resulting in: 3x = 21
• Step 2 — Divide each side by 3 resulting in x = 7
• Check your answer by substituting 7 for x in the original problem resulting in 21+20=41 which is correct.

Deductive reasoning also uses the syllogism which is a logical argument consisting of premises and a conclusion. For example:

• Premise 1 — All people die eventually.
• Premise 2 — I am a person.
• Conclusion — Therefore, I will die eventually.

Second, informal or inductive reasoning is used when there is no single correct solution to a problem. A conclusion may or may not follow from premises or facts. Consider the following:

• Observation — It has snowed in my town for the past five years during winter.
• Conclusion — It will snow this winter.

Though it has snowed for the past five years it may not this year. The conclusion does not necessarily follow from the observation. What might affect the strength of an inductive argument then? First, the number of observations is important. In our example, we are basing our conclusion on just five years of data. If the first statement said that it snowed for the past 50 years during winter, then our conclusion would be much stronger. Second, we need to consider how representative our observations are. Since they are only about our town and our conclusion only concerns it, the observations are representative. Finally, we need to examine the quality of the evidence. We could include meteorological data from those five years showing exactly how much snow we obtained. If by saying it snowed, we are talking only about a trace amount each year, though technically it did snow, this is not as strong as saying we had over a foot of snow during each year of the observation period.

Heuristics and Cognitive Errors

We use our past experiences as a guide or shortcut to make decisions quickly. These mental shortcuts are called heuristics. Though they work well, they are not fool proof. First, the availability heuristic is used when we make estimates about how often an event occurs based on how easily we can remember examples (Tversky & Kahneman, 1974). The easier we can remember examples, the more often we think the event occurs. This sounds like a correlation between events and is. The problem is that the correlation may not actually exist, called an illusory correlation.

Another commonly used heuristic is the representative heuristic or believing something comes from a larger category based on how well it represents the properties of the category. It can lead to the base rate fallacy or when we overestimate the chances that some object or event has a rare property, or we underestimate that something has a common property.

A third heuristic is the affect heuristic or thinking with our heart and not our head. As such, we are driven by emotion and not reason. Fear appeals are an example. Being reminded that we can die from lung cancer if we smoke may fill us with dread.

In terms of errors in reasoning, we sometimes tend to look back over past events and claim that we knew it all along. This is called the hindsight bias and is exemplified by knowing that a relationship would not last after a breakup. Confirmation bias occurs when we seek information and arrive at conclusions that confirm our existing beliefs. If we are in love with someone, we will only see their good qualities but after a breakup, we only see their negative qualities. Finally, mental set is when we attempt to solve a problem using what worked well in the past. Of course, what worked well then may not now and so we could miss out on a solution to the problem.