Deductive Reasoning: Definition, Application and Examples

By Indeed Editorial Team

Updated June 17, 2022 | Published May 17, 2021

Updated June 17, 2022

Published May 17, 2021

The ability to reason logically is probably the most critical aspect of problem-solving and decision making. Individuals who can put logical thinking skills to good use are, generally, considered better organizational leaders capable of identifying problems before they even arise. In most cases, only those who can logically deduce viable conclusions from all the available information can make the riskiest decisions, especially in high innovation centres. In this article, we look at several facets of deductive reasoning, a logical reasoning technique, in detail.

What is deductive reasoning?

Deductive reasoning, or deductive logic, is a type of reasoning in which a specific conclusion necessarily results from previously stated premises. In other words, the conclusion derives from two or more true statements. This approach is known to be top-down since it proceeds from widely accepted truths to draw specific logical inferences. For example, consider the following two premises or statements: A is known to be equal to B, and B is known to be equal to C. Therefore, in this context, it is necessarily true that A is also equal to C.

How does deductive reasoning work?

As indicated, the deduction process begins with a broad truth, followed by a more specific statement. A logical conclusion, then, necessarily follows from the two premises. Here is a classic example that logic scholars often use to illustrate how deductive reasoning works:

  • First premise: All men are mortal.

  • Second premise: Socrates is a man.

  • Conclusion: Therefore, Socrates is mortal.

The first premise presents the generalized, or broad, truth by indicating that all members of a class known as men are mortal. The second premise specifically identifies Socrates as a member of the class "men." Then, the conclusion logically connects the dots: if he, Socrates, is of the class of "men," he inherits mortality as an attribute of the whole class.

Generally, however, the choice of reasoning model has everything to do with the intentions of the proposer of an argument. And, on most occasions, deductive reasoning intends to present well-reasoned and verifiable arguments or decisions. Here, the arguer's objective is to provide sufficient guarantee that their conclusions are sound and valid. In other words, they choose deductive reasoning because it assures you that their inference cannot be wrong since their premises are true.

To understand how deductive logic achieves this objective, first understand the two criteria used in assessing deduction: the validity and soundness of arguments. An argument can only be valid if, and only if, its form makes it impossible to obtain a false conclusion from true premises. Otherwise, the argument will be invalid since it will not have provided a strong justification for the conclusion as expected of a deductive argument.

We should be clear that there is no degree of validity; a deductive argument is either valid or invalid. That is, it cannot be somehow valid or invalid.

For an argument to be sound, it should satisfy two requirements: first, it must be a valid argument; second, its premises must be true. Like validity, a logical argument cannot be somewhat sound: it is either sound or unsound.

One consequence of the deductive reasoning process is that the inference's validity does not guarantee the premises' truthfulness. The process only assures you that the conclusion is a logical outcome of the given premises. You don't have any information to determine if the premises are true; they could also be false. That is, the argument could be valid, although unsound. Consider the example above. If upon extensive investigation, it turns out that Socrates is a rock and not a man, the argument will be unsound, but it will still be valid.

How to apply deductive reasoning at your workplace

Several workplace scenarios require a conscious application of deductive reasoning. The situations may differ but you will most likely find it useful in solving longstanding company problems: poor sales, customer complaints or low productivity, among others. Since deductive reasoning does not allow uncertainty or guesswork, you can develop creative and decisive solutions for even seemingly endemic problems, given enough information.

In any logical thinking situation, collect as much information as possible: it is the most important thing. It allows you to develop well-grounded premises or hypotheses from which you can draw strong inferences. Hone your skills: be observational, curious and look for the smallest details in an ocean of information. Here are some of the steps you can use to apply deduction effectively:

  • Ensure you have a substantial understanding of the problem at hand, including what is precisely at stake; break it down into smaller issues if it is a complex one.

  • Analyze data relevant to the issue extensively and ask as many questions as necessary.

  • Develop a hypothesis or working assumptions or premises to guide your decision making.

  • Apply possible solutions to test the validity and soundness of your assumptions.

  • Evaluate the effectiveness of your solution by comparing it with other potential solutions.

Related: Important Types of Questioning Techniques (With Examples)

Practical examples of deductive reasoning

Here are some real-life workplace examples of deductive reasoning.

  • A beauty product innovation team, after extensive research, realizes that married working-class women abhor the more than 15 minutes it takes to apply their makeup daily. Their findings reveal that women, specifically those with young children, have no more than 10 minutes to spare on their morning makeup. The team then recommends the production of a makeup product that takes less than five minutes to apply.

  • A software company determines that products with properly written technical specifications attract more positive user recommendations. Using this information, the company's human resource director directs all software engineers to take a short technical writing course. Subsequent software products have clearer usage instructions and attract more user recommendations.

  • A local corner bakery owner finds out that most of her customers buy more of the yellow butter cake than any other. She knows she has to stock more of the yellow butter cake and bake the best in town. She hires additional bakers, one of whom has a glowing reputation.

  • After an influx of customer complaints about poor response times, a company's customer service department has to improve its performance. The department decides to hire two more customer service experts; this results in increased customer satisfaction.

Deductive vs. inductive reasoning

Unlike deductive reasoning, where the conclusion's truth is sufficiently guaranteed as long as the premises are true, inductive arguments are uncertain. The inference could be true, and there is some data to back it up, but it may as well be false. In other words, in inductive reasoning, the premises only serve to give a limited measure of validity, not all.

Inductive reasoning uses the bottom-up approach: you start with specific data, from which you derive a general conclusion. You try to find out the theory that explains the data, but the data can lead to different conclusions, or the inferences can change with new evidence. Consider this example: Gerald is a grandfather. Gerald is bald. Therefore, all grandfathers are bald. Here, although the inference is probably true, it does not necessarily follow from the premises. The premises provide some validity since we have a bald grandfather. However, the conclusion could change if another grandfather, who is not bald, shows up.

Related: Inductive Reasoning vs. Deductive Reasoning (With Examples)

Types of deductive reasoning

There are three types of deductive reasoning: syllogism, modus ponens, and modus tollens. We explain each of them in detail below.

Syllogism

A syllogism is the most common and, probably, simplest type of deductive reasoning. It connects the dots between two statements and makes a logical inference. In its simplest form, it states that if X=Y and Y=Z, then X=Z. A more practical example would be: All mammals have mammary glands; bats are mammals; therefore, bats have mammary glands.

While using more premises is possible, a syllogism is primarily a three-part valid argument. The more general statement is the major premise, “all mammals have mammary glands.” The more specific statement, “bats are mammals,” is known as the minor premise. And the conclusion is a logical connection between the two hypotheses.

Modus ponens

A modus ponens, sometimes known as “Affirming the Antecedent” or “Law of Detachment,” is a form of valid logical reasoning. Here, a deduction involves the usual parts presented differently: a conditional statement of the form if X then Y; an antecedent of the conditional statement; and a consequent of the conditional statement. A practical example will be: if it has four legs, then it is a cow; it has four legs; so, it is a cow.

Modus tollens

A modus tollens, or Denying the Consequent, is the exact opposite of a modus ponens. Like the latter, it has two premises: a conditional statement of the form if X then Y; the antecedent, unlike in a modus ponens, is a refutation of the consequent—a statement of the form, not Y. Consider this example: if it has four legs, then it is a cow; it does not have four legs; so, it is not a cow.

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