Reasoning is a mental activity that consists of organizing information or beliefs into a series of steps in order to reach conclusions. Not surprisingly, sometimes our reasoning seems sensible and straightforward, and other times it seems a little off. Consider some reasons offered by people who filed actual insurance accident claims (www.swapmeetdave.com):

When people like these hapless drivers argue with you in a way that seems inconsistent or poorly thought out, you may accuse them of being “illogical.” Logic is a system of rules that specifies which conclusions follow from a set of statements. To put it another way, if you know that a given set of statements is true, logic will tell you which other statements must also be true. If the statement “Jack and Jill went up the hill” is true, then according to the rules of logic, the statement “Jill went up the hill” must also be true. To accept the truth of the first statement while denying the truth of the second statement would be a contradiction. Logic is a tool for evaluating reasoning, but it should not be confused with the process of reasoning itself. Equating logic and reasoning would be like equating carpenter’s tools (logic) with building a house (reasoning).

Earlier in the chapter, we discussed decision making, which often depends on reasoning with probabilities. Practical reasoning and theoretical reasoning also allow us to make decisions (Walton, 1990). Practical reasoning is figuring out what to do, or reasoning directed toward action. Means–ends analysis is one kind of practical reasoning. An example is figuring out how to get to a concert across town if you do not have a car. In contrast, theoretical reasoning (also called discursive reasoning) is reasoning directed toward arriving at a belief. We use theoretical reasoning when we try to determine which beliefs follow logically from other beliefs.

389

Suppose you asked your friend Bruce to take you to a concert, and he said that his car was not working. You would undoubtedly find another way to get to the concert. If you then spied him driving into the concert parking lot, you might reason: “Bruce told me his car was not working. He just drove into the parking lot. If his car was not working, he could not drive it here. So, either he suddenly fixed it, or he was lying to me. If he was lying to me, he’s not much of a friend.” Notice the absence of an action-oriented goal. Theoretical reasoning is just a series of inferences concluding in a belief—in this case, about your so-called friend’s unfriendliness!

If you concluded from these examples that we are equally adept at both types of reasoning, experimental evidence suggests you are wrong. People generally find figuring out what to do easier than deciding which beliefs follow logically from other beliefs. In cross-cultural studies, this tendency to respond practically when theoretical reasoning is sought has been demonstrated in individuals without schooling. Consider, for example, this dialogue between a Nigerian rice farmer, a member of the preliterate Kpelle people, and an American researcher (Scribner, 1975, p. 155):

As this excerpt shows, the farmer does not seem to understand that the problem can be resolved with theoretical reasoning. Instead, he is concerned with retrieving and verifying facts, a strategy that does not work for this type of task.

A very different picture emerges when members of preliterate cultures are given tasks that require practical reasoning. One well-known study of rural Kenyans illustrates a typical result (Harkness, Edwards, & Super, 1981). The problem describes a dilemma in which a boy must decide whether to obey his father and give the family some of the money he has earned, even though his father previously promised that the boy could keep it all. After hearing the dilemma, the participants were asked what the boy should do. Here is a typical response from a villager:

A child has to give you what you ask for just in the same way as when he asks for anything you give it to him. Why then should he be selfish with what he has? A parent loves his child and maybe the son refused without knowing the need of helping his father. … By showing respect to one another, friendship between us is assured, and as a result this will increase the prosperity of our family.

This preliterate individual had little difficulty understanding this practical problem. His response is intelligent, insightful, and well reasoned. A principal finding from this kind of cross-cultural research is that the appearance of competency on reasoning tests depends more on whether the task makes sense to participants than on their problem-solving ability.

Educated individuals in industrial societies are prone to similar failures in reasoning, as illustrated by belief bias: People’s judgments about whether to accept conclusions depend more on how believable the conclusions are than on whether the arguments are logically valid (Evans, Barston, & Pollard, 1983) (see also The Real World box). For example, syllogistic reasoning assesses whether a conclusion follows from two statements that are assumed to be true. Consider the two following syllogisms, evaluate the argument, and ask yourself whether or not the conclusions must be true if the statements are true:

390

Syllogism 1

391

Syllogism 2

If you are like most people, you probably concluded that the reasoning is valid in Syllogism 1 but flawed in Syllogism 2. Indeed, researchers found that nearly 100 percent of participants accepted the first conclusion as valid, but fewer than half accepted the second (Evans, Barston, & Pollard, 1983). But notice that the syllogisms are in exactly the same form. This form of syllogism is valid, so both conclusions are valid. Evidently, the believability of the conclusions influences people’s judgments.

Research using fMRI provides novel insights into belief biases on reasoning tasks. In belief-laden trials, participants were scanned while they reasoned about syllogisms that could be influenced by knowledge affecting the believability of the conclusions. In belief-neutral trials, syllogisms contained obscure terms whose meanings were unknown to participants, as in the following example:

Syllogism 3

Belief-neutral reasoning activated different brain regions than did belief-laden reasoning (as shown in FIGURE 9.22). Activity in a part of the left temporal lobe involved in retrieving and selecting facts from long-term memory increased during belief-laden reasoning. In contrast, that part of the brain showed little activity and parts of the parietal lobe involved in mathematical reasoning and spatial representation showed greater activity during belief-neutral reasoning (Goel & Dolan, 2003). This evidence suggests that participants took different approaches to the two types of reasoning tasks, relying on previously encoded memories in belief-laden reasoning and on more abstract thought processes in belief-neutral reasoning. These findings fit with other results from neuroimaging studies indicating that there is no single reasoning centre in the brain; different types of reasoning tasks call on distinct processes that are associated with different brain regions (Goel, 2007).

392