A 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 is that which is based on two premises that are related by 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 proves that a logical process has been followed. However, the premises do not offer evidence that proves the veracity of the conclusions. Take the following example into account:
When it's cold, my mom wears her favorite scarf. Today is cold. So, my mom will wear her favorite scarf today.
The line of reasoning that follows is correct. However, it is not known if it is true that"today is cold". If the person who has uttered the deduction is lying, then the conclusion can not be more than incorrect.
List of examples of deductive reasoning
Examples with two premises and one 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 the 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.
Below 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: The squares are rectangles.
Conclusion: The squares have four sides.3
3-Premise I: All numbers ending 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 meats are 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 breast milk.
Premise II: Dolphins are mammals.
Conclusion: Dolphins feed their young with breast milk.
9-Premise I: Plants perform the process of photosynthesis.
Premise II: Hydrangeas are plants.
Conclusion: Hydrangeas perform photosynthesis.
10-Premise I: Dicotyledonous plants have two cotyledons.
Premise II: Magnolias are dicotyledons.
Conclusion: 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 is not usually grouped 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 flu, they talk 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: Then 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 able to play 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 syllogism model. In these cases, one of the premises is omitted because it is considered that this is obvious or that 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 grunting all day, do not go near him or he 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 absent premises. The result would be as follows:
Premise I: When my dog is angry, it can bite people.
Premise II: My dog is mad at you.
Conclusion: My dog could bite you at any time.
2- Be careful with the bees, they could sting you.
The premise is that bees sting.
3- The apple fell by the effect of gravity.
Here it is assumed that the interlocutor knows that gravity attracts objects towards the center of the Earth.
4- It takes me an hour to go from my house to college.
That is why I will arrive at 7:30. In this case, it can be assumed that whoever proposes the reasoning will leave his house at 6:30.
5- It is necessary to remove the cat 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