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When Should a Teacher Use Deductive Reasoning?

As a student, you got some confusing ideas at school. We learned about a mammal’s features, like hair, and then we were told a dolphin is a mammal, even though it is not hairy or furry. This is where deductive reasoning comes in.

A teacher should use deductive reasoning when they want to show the validity and soundness of a hypothesis. Deductive reasoning encourages students to prove or disprove a theory through research. You might assume that deductive reasoning is most applicable in logic-based subjects, but the skill is appropriate in all spaces.

Deductive reasoning can be a fantastic classroom tool. To learn more, keep reading.

Why Should a Teacher Use Deductive Reasoning?

Deductive reasoning teaches students how to think critically. It allows them to create links and, instead of making assumptions, find proof for their hypotheses through reasoning and sound arguments.

Teachers need to teach students what sound deductive reasoning is. Because deductive reasoning is a relatively simple concept, you can use it to make silly or nonsensical arguments, but you should avoid that.

When using deductive reasoning, you are presenting a hypothesis and providing evidence of why that hypothesis may be true or false. The simplest form of deductive reasoning is a “premise-premise-conclusion” format.

For example, let us start with a simple premise:

  • My stomach starts to feel strange when I drink milk and eat cheese.

We can then combine it with a second premise:

  • My stomach feels fine when I drink water or juice.

Therefore, the conclusion would be:

  • I may be lactose intolerant due to my reaction only to dairy-based products.

What is Deductive Reasoning?

Deductive reasoning is a logical method of creating specific conclusions. When using deductive reasoning, you start with simple ideas which are pretty broad, and you slowly narrow them until you reach more exact conclusions.

When you look at the phrasing, it guides you toward the process. “Deductive” comes from the root word “deduct, ” meaning to remove. This shows how the procedure involves the elimination of non-vital ideas or variables.

We also call deductive reasoning “top-down reasoning,” as it functions like an upside-down pyramid where you move from many ideas to one or two ideas. Another synonym is “deductive logic.” The opposite of this reasoning is inductive reasoning. 

To explain deductive reasoning, it’s better to begin with an example. To do this, we will use a “premise-premise-conclusion” approach again.

  • Premise: Only people over 18 are allowed to vote.
  • Premise: I voted in the last election.
  • Conclusion: Therefore, I must be older than 18 years.

Looking at the above example, it makes sense that we have one scenario or premise. Then another variable is thrown in as the second premise, and we combine them to reach a logical conclusion.

  • Premise: All mammals give birth to live young.
  • Premise: Dolphins give birth to live young.
  • Conclusion: Therefore, a dolphin is a mammal.

In the real world, you use deductive reasoning for everything from problem-solving issues at home to the workplace to solving puzzles and remembering where you left your keys.

  • Premise: I last had my keys when I walked into the kitchen.
  • Premise: I went straight to the fridge for a snack and didn’t have my keys when I left.
  • Conclusion: Therefore, my keys are somewhere close to the fridge.

However, not all arguments using deductive reasoning are logical, so teachers who use deductive reasoning must do so logically. We can do this by examining the soundness and validity of arguments.

Valid and Sound Deductive Reasoning

When using deductive reasoning, you must ensure that the argument is both valid and sound. Validity refers to truthful premises that have a relation to one another. However, the argument becomes invalid if their relationship is not logical (source).

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  • Premise: Tigers have stripes.
  • Premise: The zebra at the zoo has stripes.
  • Conclusion: Therefore, the zebra is a tiger.

As you can see in the above argument, while both premises are valid and truthful, their relationship with each other does not make sense. Several elements make a tiger a predatory jungle cat, and those characteristics do not belong to a zebra, so the argument must be invalid.

On the other hand, unsound arguments refer to untruthful premises. So let’s examine a possible scenario.

  • Premise: All women like to shop.
  • Premise: Jason likes to shop.
  • Conclusion: Therefore, Jason is a woman.

As you can see, the above scenario is invalid and unsound. Firstly, it is not true to say that all women like to shop. This is a stereotypical generalization. In contrast, the statement about Jason might be accurate, but the connection does not make sense, making the argument invalid.

Unsound and invalid arguments are known as fallacies (source). While fallacies may look logical at first glance, they cannot make sense because they are generalized or stereotypical information.

Combined, this unsound and invalid deductive reasoning leads to a false conclusion. Therefore, when teachers use deductive reasoning in class, it has to be carefully monitored. 

Inductive Reasoning

If you come across deductive reasoning, you will soon encounter inductive reasoning. Inductive reasoning is when you take more specific concepts and build them together to reach broader conclusions.

In essence, inductive reasoning is the opposite of deductive reasoning. 

In a scenario where you might use inductive reasoning, you would use a similar format to the “premise-premise-conclusion” format, but your premise would have to be more specific.

  • Premise: My birthday is on the 30th of January.
  • Premise: My neighbor’s birthday is also on the 30th of January.
  • Conclusion: The 30th of January is the most common birthday.

As you can see in the above example, the premise we used is specific, and because of that, the conclusion you reach may not be the most logical. Therefore, inductive reasoning best uses as many samples or data points as possible (source).

Real-world examples of inductive reasoning are in spaces like data analysis, market research, and population surveys. We can come up with broad conclusions that make sense for most people through lots of specific data.

Another way to differentiate between inductive and deductive reasoning is that inductive reasoning creates assumptions about a situation that may be correct, while deductive reasoning should provide a fact.

How Should a Teacher Use Deductive Reasoning?

We commonly use deductive reasoning techniques in the classroom. When using deductive reasoning, the teacher will present rules, provide examples, and allow students to practice applying those rules to other models or scenarios (source).

It is likely that your teacher also used deductive reasoning in your classroom. For example, in English Language Arts, you probably saw teachers supplying you with spelling rules like “I before E except after C.”

Next, your teachers would provide examples of words that followed that rule, like “tie,” “piece,” “niece,” and “variety.” Then, for the second part of the rule, you would use examples like “receive,” “deceit,” and “ceiling.”

In this example, deductive reasoning would look like the one below.

  • Premise: “I” comes before “e” except after “c.”
  • Premise: I spell the word “alienate” using that rule.
  • Conclusion: Therefore, my spelling is correct.

Deductive reasoning can be instrumental as long as you use it logically. However, you can use the same rules and misapply them to a scenario.

  • Premise: “I” comes before “e” except after “c.”
  • Premise: I spell the word “wierd” using that rule.
  • Conclusion: Therefore, my spelling is correct.

However, in the above example, the conclusion is incorrect because “weird” is one of the exceptions to that rule. Deductive reasoning is sometimes instrumental, but you must apply it carefully as there may be issues with soundness and validity.

Considerations for Teaching Deductive Reasoning

Deductive reasoning must be taught and practiced like any other skill in school. You cannot expect a student to automatically understand the connections between two elements and how they affect the outcome.

Therefore, when teaching deductive reasoning, you need to consider the following elements:

Teaching ElementExplanation
When starting to teach, use examples that students will understand.This means digging into their contextual knowledge and frame of reference.
Scaffold examples as they increase in complexity.Giving students the most challenging example will likely confuse them, so the information needs to be built up slowly and methodically.
Focus on overarching ideas.Instead of focusing on the more specific questions, start broad and become more exact as students’ abilities develop.

Useful Examples of Deductive Reasoning

You can use deductive reasoning in several ways in the classroom. The method does not need changing, but you can change the content to suit the subject. 

For mathematics, you might use deductive reasoning like this:

  • Premise: All triangles have three sides.
  • Premise: This shape has three sides.
  • Conclusion: Therefore, this shape is a triangle.

The above would work well for an elementary classroom, but you can change the premises for middle and high school students.

  • Premise: An isosceles triangle has at least two sides equal in length.
  • Premise: This triangle has two sides, each 3 inches long.
  • Conclusion: Therefore, this triangle is an isosceles triangle.

In a history classroom, you may try to use deductive reasoning to explain why an event came to pass.

Premise:The USA and UK are part of the United Nations Security Council.
Premise:In 2022, the UN Security Council voted unanimously against the proliferation of weapons of mass destruction.
Conclusion:Therefore, the USA and UK voted against weapons of mass destruction.

If you were using deductive reasoning in a chemistry classroom, your work might look something like the premises below:

  • Premise: All noble gases are stable.
  • Premise: Argon is a noble gas.
  • Conclusion: Therefore, argon is stable.

You can use deductive reasoning across various subjects and fields if you provide the correct premises for students to work with and explore.

ELA English Language Arts

English Language Arts is the branch of English teaching and instruction that deals with language. It focuses on English reading, writing, listening, and speaking. 

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Deductive reasoning can be beneficial in an English classroom because, despite the notion that English is a creative subject, there are many rules and patterns within the language. This includes rules around spelling, grammar, and punctuation.

Some teachers might need help presenting texts to students in the ELA class. How much of the lesson should you spend on analysis before finding the main point and purpose of the text? To find some guidance, read When Should Teachers Introduce the Purpose of a Text?

Even in literature, you can use deductive reasoning to create links between characters.

  • Premise: Romeo is a Montague.
  • Premise: Benvolio is also a Montague.
  • Conclusion: Therefore, Benvolio is related to Romeo.

We have explored some examples of spelling rules earlier and how deductive reasoning would apply to them. We can use something similar for grammatical rules. This should help students apply their understanding of sentence types and structure.

An English teacher explains the following premises:

  • Premise: A sentence in active voice follows the subject, verb, and object order.
  • Premise: A sentence in passive voice follows the order of object, verb, and subject.

Then the teacher puts “The cat is loved by all” on the board and asks her students to identify whether the sentence uses the active or passive voice. After comparing the sentence with the premises, the students can conclude the following:

  • Conclusion: The sentence cannot be in active voice as the object comes first.

Another example is applying the rules of punctuation through deductive reasoning. An English teacher would start by presenting these premises:

  • Premise: Parentheses show related, non-essential elements.
  • Premise: Parenthetical punctuation always uses commas, brackets, and dashes.

She then presents her students with an example sentence: “My mother, a woman of strong character with a sharp tongue, recently called me.” The students will then determine whether the sentence correctly uses parenthetical punctuation.

  • Conclusion: The sentence uses commas correctly. 

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English Language Arts covers such a broad base of topics that deductive reasoning is the clear choice in working on patterns and rules in the language.

Final Thoughts

Deductive reasoning is a beneficial skill to have in one’s teaching arsenal. You can use it to help students work through concepts, create links and find the relationships in cause-and-effect scenarios.

Deductive reasoning is the building block for logic-based reasoning. We use deductive reasoning to solve problems and draw inferences, even for fun.

Without it, how would we solve that murder mystery in the latest episode of CSI? Or know that dolphins actually have fur around their blowholes, making them fulfill the requirements of a mammal?