- List of examples of deductive reasoning
- Examples with two premises and a conclusion
- Examples that do not follow the traditional model
- References
An example of deductive reasoning is if A is B, and B is C, then A is C. From this example, it can be seen that deductive reasoning are those that are based on two premises that are related thanks to a conclusion. If the premises are correct then the conclusion will be correct as well.
In this sense, the premises of deductive reasoning are intended to provide sufficiently truthful and verifiable evidence to support the conclusion.
Sometimes deductive reasoning shows that a logical process has been followed. However, the premises do not offer evidence to prove the veracity of the conclusions. Consider the following example:
The line of reasoning followed is correct. However, it is not known whether it is true that "today is cold". If the person who has stated the deduction is lying, then the conclusion cannot be more than incorrect.
List of examples of deductive reasoning
Examples with two premises and a conclusion
Traditional deductive reasoning follows the model "if A is B and B is C, then A is C". That is, they consist of two premises and a conclusion.
One of the premises is general while the other is more specific. The first is called a universal proposition, while the second is known as a specific statement.
This is known as a syllogism and was introduced by Aristotle. According to the Greek philosopher, this type of reasoning demonstrates a high level of evaluation of the premises.
Here are 20 examples of this type of deductive reasoning.
1-Premise I: All human beings are mortal.
Premise II: Aristotle is a human being.
Conclusion: Aristotle is mortal.
2-Premise I: All rectangles have four sides.
Premise II: Squares are rectangles.
Conclusion: Squares have four sides.3
3-Premise I: All numbers that end in 0 or 5 are divisible by 5.
Premise II: The number 455 ends in 5.
Conclusion: The number 455 is divisible by 5.
4-Premise I: All birds have feathers.
Premise II: Nightingales are birds.
Conclusion: Nightingales have feathers.
5-Premise I: Reptiles are cold-blooded animals.
Premise II: Snakes are reptiles.
Conclusion: Snakes are cold-blooded animals.
6-Premise I: All cells contain deoxyribonucleic acid.
Premise II: I have cells in my body.
Conclusion: I have deoxyribonucleic acid.
7-Premise I: Red meat is rich in iron.
Premise II: The steak is a red meat.
Conclusion: The steak is rich in iron.
8-Premise I: Mammals feed their young with mother's milk.
Premise II: Dolphins are mammals.
Conclusion: Dolphins feed their young with mother's milk.
9-Premise I: Plants carry out the process of photosynthesis.
Premise II: Hydrangeas are plants.
Conclusion: Hydrangeas carry out photosynthesis.
10-Premise I: Dicotyledonous plants have two cotyledons.
Premise II: Magnolias are dicotyledonous.
Bottom Line: Magnolias have two cotyledons.
11-Premise I: All cars have at least two doors.
Premise II: The Prius is a car.
Conclusion: The Prius has at least two doors.
12-Premise I: Noble gases are not usually grouped with other elements.
Premise II: Xenon is a noble gas.
Conclusion: Xenon does not usually group with other elements.
13-Premise I: Grains are rich in vitamin B.
Premise II: Lentils are grains.
Conclusion: Lentils are rich in vitamin B.
14-Premise I: When people have the flu, they speak nasally.
Premise II: I have the flu.
Conclusion: Since I have the flu, I am speaking nasally.
15-Premise I: The planets are spherical.
Premise II: Mars is a planet.
Conclusion: Mars is spherical.
16-Premise I: The stars have their own light.
Premise II: The Sun is a star.
Conclusion: The Sun has its own light.
18-Premise I: My sister opens her umbrella only when it is raining.
Premise II: My sister has opened her umbrella.
Conclusion: So, it is raining.
19-Premise I: When John is sick, he does not go to work.
Premise II: John is sick today.
Conclusion: Today John will not go to work.
20-Premise I: My teacher is capable of playing any wind instrument correctly.
Premise II: The flute is a wind instrument.
Conclusion: My teacher is able to play the flute correctly.
Examples that do not follow the traditional model
Some deductive reasoning does not follow the model of the syllogism. In these cases, one of the premises is omitted because it is considered obvious or can be inferred from the rest of the statement. For this reason, this type of deductive reasoning is more difficult to recognize.
Some examples of this type of reasoning are:
1- The dog has been growling at you all day, do not approach it or it will bite you.
In this case, it is inferred that the dog is angry and that if it is angry, it can bite you.
This example can be reformulated as a syllogism, highlighting the missing premises. The result would be the following:
Premise I: When my dog is angry, he can bite people.
Premise II: My dog is mad at you.
Conclusion: My dog could bite you at any moment.
2- Be careful with bees, they could sting you.
The unspoken premise is that bees sting.
3- The apple fell due to the effect of gravity.
Here it is assumed that the interlocutor knows that gravity pulls objects towards the center of the Earth.
4- It takes me an hour to go from my house to the university.
Therefore, I will arrive at 7:30. In this case, it can be assumed that the person proposing the reasoning will leave their house at 6:30.
5- It is necessary to get the cat to pass before it begins to scratch the door.
From here, it can be understood that the cat scratches the door when it wants to go for a walk.
References
- Deductive and Inductive Arguments. Retrieved on October 6, 2017, from iep.utm.edu
- Deductive and Inductive Arguments. Retrieved on October 6, 2017, from lanecc.edu
- Deductive and Inductive Arguments: What's the Difference. Retrieved on October 6, 2017, from thoughtco.com
- Deductive Arguments and Valid Reasoning. Retrieved on October 6, 2017, from criticalthinkeracademy.com
- Deductive reasoning. Retrieved on October 6, 2017, from wikipedia, org
- Definition and Examples of Deductive Arguments. Retrieved on October 6, 2017, from thoughtco.com
- What is deductive argument? Retrieved on October 6, 2017, from whatis.techtarget.com