The Differences Between Logic and Reasoning

When I first began planning the contents of my book Method Matters: A Practical Guide to Achieving Your Goals Through Critical Thinking, I spent a great deal of time weighing the costs and benefits of including a chapter that focuses purely on logic. The terms logic and reasoning are often used interchangeably, but they actually describe two different things. Let’s briefly define these two terms to show their differences:

• • Logic is the process of working through inferences from a set of facts to draw a conclusion while avoiding logical fallacies. Structure is very important.

• • Reasoning is the process of using logic in tandem with the context of the real world. This includes the facts of a situation and available information, as well as beliefs, desires, emotions, uncertainties, goals, and a wide variety of other concerns.

Essentially, reasoning is the real-world application of logic in conjunction with real-world circumstances. It is possible for someone to have good reasoning abilities without ever studying logic or even putting much thought into logic at all. It’s also possible for someone who has strong roots in logical thinking to easily mess up the other parts that go into reasoning.

Let’s briefly discuss a scenario that requires overall reasoning abilities without the need for an understanding of logic. Imagine you’re at a crossroads in your career. You have to decide whether to stay in your current job, which offers stability and familiarity, but limited growth opportunities, or to accept a new job offer that promises better career growth but comes with the risk of the unknown and the potential for a more challenging work-life balance. You will need to take a myriad of factors into consideration, such as family circumstances, short term and long term salary, importance of work-life balance, and your level of risk aversion. You’ll also need to ensure you don’t let emotions play too large a role in your decision, though it certainly does have a place. Making the right choice would be very difficult, but that difficulty doesn’t involve much logical reasoning. You wouldn’t need to worry about something like denying the antecedent or fallacy of the undistributed middle.

To contrast, let’s discuss a scenario that does require skills in logical thinking but not overall reasoning. Imagine that you are shown a set of four cards placed on a table, each of which has a number on one side and a color on the other. The visible faces of the cards show 7, 4, green and blue. There’s a rule that every card that has an even number on one side must have the color blue on the other side. Which card, or cards, do you need to flip to test that each card follows that rule? In other words, which cards do you have to flip to find any cards that might violate the rule?

This is a version of a logic puzzle called the Wason Selection Task given to participants of a study in 1966. Less than 10% of participants found the correct solution. Let’s go over the solution here by assessing each card one-by-one:

1. 1. The first card is number-face-up and shows a 7. Since this card is odd, the rule doesn’t apply to it, so we don’t need to turn it over.
   2. The second card is number-face-up and shows a 4. Since this card is even, the rule does apply to it, so you need to turn it over to see if the back is blue.
   3. The third card is color-face-up and is green. Since the number side is face down, we don’t know if the number on this card is even or odd. If it’s even, it would violate the rule that the color must be blue, so we do need to turn it over to check.
   4. The fourth card is color-face-up and is blue. If the number on the other side is even, then this card follows the rule. If it’s odd, then the rule doesn’t apply to this card. Therefore, you don’t need to turn it over.

Generally, people would correctly determine that we do need to turn over card 2, but would incorrectly state that we don’t need to turn over card 3 and do need to turn over card 4 instead. In the original Wason experiment, they also found that if a more familiar example were given in place of the cards, such as “if you are drinking alcohol, then you must be over 18” and uses cards with ages and beverages instead of numbers and colors, the participants fared better. This reveals an interesting relationship between logic and rationality. In some cases, strong abilities in one can make up for weaker abilities in the other.