A deductive argument is one that seeks to guarantee the validity of the reasoning by pointing out that the conclusion reached is true because the premises (the arguments that precede the conclusion) are also true.
An example of this type of argument is: all dogs are mammals, all mammals have lungs; therefore all dogs have lungs. Another example: Daisies are plants and all plants photosynthesize; therefore, daisies photosynthesize.
An argument in which the conclusion correctly derives from the premises is "deductively valid." If a valid argument has premises that can be confirmed to be true, the argument will be sound. Let's see this explanation with an example:
The two premises guarantee the veracity of the conclusion, since this is the result of logical reasoning. However, the argument has not presented information that allows us to establish whether the two premises are true, so it is not solid.
If it is the case that either of the two premises is not true, this will not change the fact that it is a valid argument.
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Arguments in logic were first studied by the Greek philosopher Aristotle. This established the difference between deductive and inductive arguments and, in this sense, indicated that deductive arguments are or are not valid, while inductive ones present degrees of acceptance, are probable or unlikely..
It also pointed out that, in deductive arguments, the speaker considers that the veracity of the premises also ensures the veracity of the conclusion.
The typical pattern of deductive arguments is: if A is B and B is C, then A is C. When the deductive argument follows this pattern, it is called a "syllogism".
The syllogisms present two premises and a conclusion; the first premise is called a universal proposition and the second is known as a specific statement.
For example:
However, not all arguments are presented in this way. For example, if they tell us to be careful about being around bees, because they can sting you. In this example it is understood that all bees sting.
1 - Premise I: All men are mortal.
Premise II: Aristotle is a man.
Conclusion: Aristotle is mortal.
2 - Premise I: Donna is sick.
Premise II: If Donna is sick, she won't be able to attend today's meeting.
Conclusion: Donna will not be able to attend today's meeting.
3 - Premise I: A equals B.
Premise II: B equals C.
Conclusion: So, A equals C.
4 - Premise I: Dolphins are mammals.
Premise II: Mammals have kidneys.
Conclusion: So all dolphins have kidneys.
5 - Premise I: All numbers ending in 0 or 5 are divisible by 5.
Premise II: 35 ends in 5.
Conclusion: 35 is divisible by 5.
6 - Premise I: In order to graduate, students must have 32 approved credits.
Premise II: Monica has 40 approved credits.
Conclusion: Monica will graduate.
7 - Premise I: All birds have feathers.
Premise II: Nightingales are birds.
Conclusion: Nightingales have feathers.
8 - Premise I: All cats have a highly developed sense of smell.
Premise II: Garfield is a cat.
Conclusion: Garfield has a developed sense of smell.
9 - Premise I: Reptiles are cold-blooded animals.
Premise II: Snakes are reptiles.
Conclusion: snakes are cold blooded.
10 - Premise I: Cacti are plants.
Premise II: Plants carry out the photosynthesis process.
Conclusion: Cacti effect photosynthesis.
11 - Premise I: Red meat is rich in iron.
Premise II: The steak is a red meat.
Bottom Line: Steak Contains Iron.
12 - Premise I: Acute angles are less than 90 °.
Premise II: The angles of an equilateral triangle measure 60 °.
Conclusion: The angles of an equilateral triangle are acute.
13 - Premise I: All noble gases are stable.
Premise II: Helium is a noble gas.
Conclusion: Helium is stable.
14 - Premise I: Magnolias are dicotyledonous.
Premise II: Dicots have seeds with two embryos.
Conclusion: Magnolias have seeds with two embryos.
15 - Premise I: All human beings are free.
Premise II: Ana is a human being.
Conclusion: Ana is free.
16 - Premise I: All cells contain deoxyribonucleic acid (DNA).
Premise II: Elephants have cells in their bodies.
Bottom Line: Elephants have deoxyribonucleic acid (DNA).
17 - Premise I: It takes an hour to get to the mall from my house.
Premise II: I will leave my house at 5:00 PM.
Conclusion: I will arrive at the mall at 6:00 PM.
18 - Premise I: When my dog gets angry, he bites.
Premise II: My dog is angry.
Conclusion: My dog is going to bite me.
19 - Premise I: There are three people in my family.
Premise II: Every member of my family is tall.
Conclusion: All members of my family are tall.
20 - Premise I: Gravity draws objects towards the center of planet Earth.
Premise II: Apples Fall Down.
Conclusion: Apples are attracted by gravity.
21 - Premise I: This dog always barks when someone is at the door.
Premise II: The dog has not barked.
Conclusion: So, there is no one at the door.
22 - Premise I: Sam is always where Ben is.
Premise II: Sam is in the library.
Conclusion: So Ben is also in the library.
23 - Premise I: Citrus fruits are rich in vitamin C.
Premise II: Lemon is a citrus.
Conclusion: Lemon is rich in vitamin C.
24 - Premise I: I shouldn't go to work on Sunday.
Premise II: I must go to work today.
Conclusion: So, today is not Sunday.
25 - Premise I: Planets are round.
Premise II: Earth is a planet.
Conclusion: The Earth is round.
Probabilistic argument.
Inductive argument.
Analog argument.
Conductive argument.
Argument from authority.
Abductive argument.
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2. Deductive and Inductive Arguments: What's the Difference? (2017) Retrieved on May 31, 2017, from thoughtco.com.
3. Definition and Examples of Deductive Arguments, Retrieved on May 31, 2017, from thoughtco.com.
4. What is deductive argument? Retrieved on May 31, 2017, from whatis.techtarget.com.
5. Deductive and Inductive Arguments. Retrieved on May 31, 2017, from lanecc.edu.
6. Deductive Arguments and Valid Reasoning. Retrieved on May 31, 2017, from criticalthinkeracademy.com.
7. Deduction and Induction. Retrieved on May 31, 2017, from butte.edu.
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