Inductive and Deductive Reasoning

1. Inductive and Deductive
Logic
Jay Vaughn G. Pelonio, M.A.
Teacher 1

2. Short Quiz
If p, then q
p
q

3. What is an Argument?
Argument is:
1. a series of statements that aims to determine the degree of
truth of a conclusion
2. a set of reasons with the aim to persuade others that a
statement is correct

4. Parts of an Argument
An argument has two parts:
Premise/s; Conclusion
p → q ------------- premise 1
p ------------- premise 2
__________
∴ q ------------- conclusion

5. Inductive and Deductive Reasoning
These methods of reasoning are somewhat similar but there are at
least two differences between them:
a. format
b. strength of the conclusion

6. Inductive Argument
Examine the argument below:
1. Orange is a fruit
2. A box is full of fruits
3. Therefore, the box is full of oranges

7. Inductive Argument (cont.)
If we assume that premise 1 and 2 are correct, are we sure that the
conclusion is also correct?
The answer is no – a box full of fruits might contain something else.

8. Inductive Argument (cont.)
Try another example:
1. Mr. Bean wears leather shoes on Monday
2. Mr. Bean wears leather shoes on Tuesday
3. Mr. Bean wears leather shoes on Thursday
4. So, Mr. Bean wears leather shoes on weekdays.
Even if we assume the premises are true, we still cannot be certain that
the conclusion is always true.

9. Inductive Argument (cont.)
Based on the previous examples, we can infer that:
Inductive Arguments are only “probable”, not conclusive.

10. Inductive Argument (cont.)
Definition:
an argument that is constructed in a way that if the premises are true,
it is unlikely that the conclusion is false.
1. Brownie is a calm and gentle dog.
2. Brownie didn’t bite me when I passed by this morning.
3. Therefore, Brownie will not bite me if I pass by in the future.

11. Deductive Argument
Examine this argument below:
1. If it rains, then the cities will be flooded.
2. It rained. _
3. Therefore, the cities will be flooded.
If we assume 1 and 2 are true, then we can be quite sure that the
conclusion is also true.

12. Deductive Argument (cont.)
Definition:
Deductive Argument is an argument so constructed in a way that if the
premises are true, then there is no way that the conclusion is false.
1. Organic matter produce CO2 if used as fuel
2. Coal is an organic matter.
3. Therefore, coal will produce CO2 if used as fuel.

13. Deductive vs Inductive
Deductive Inductive
Strength of Conclusion Conclusive Highly Probable
Purpose Prove or disprove a statement Argue that a statement may be
possible
Format General idea → Specific Conclusion Specific Idea → General Conclusion

14. Valid and Sound Logic
Deductive arguments, as powerful as it may be, are often used the
wrong way – and people are often misled as a result:
1. Monkeys like to eat bananas.
2. Juan dela Cruz likes to eat bananas.
3. Therefore, Juan dela Cruz is a monkey.
Do you see what is wrong with the argument?

15. Valid Arguments:
Arguments that are correctly constructed, in a way that if all of the
premised are true, then there is no way the conclusion is false.
Let us examine another invalid deductive argument:
1. If it is a weekday, then the shops are open
2. The shops are closed.
3. It is a weekend.
Why is it invalid?

16. Activity
List at least five (5) possible reasons “why a shop is closed”
1. _______________________________________________________
2. _______________________________________________________
3. _______________________________________________________
4. _______________________________________________________
5. _______________________________________________________

17. Sound Arguments
Sound Arguments are valid arguments, that have correct premises.
1. Anything that meows is a cat.
2. My dog meows.
3. Therefore, my dog is a cat.
What is wrong with this argument?

18. Activity
Determine if the following arguments are Deductive or Inductive

19. Activity
Use deductive to prove the following facts. Make sure that your logic is
sound.
Example:
Prove that plants are not animals.
1. Plants are organisms that produce their own food.
2. Animals do not produce their own food.
3. So, plants are not animals.

20. Activity
a. Cellular phones are electronic devices
1._______________________________________________________
2._______________________________________________________
3. Therefore, Cellular phones are electronic devices.

21. Activity
b. pi (∏) is an irrational number
1._______________________________________________________
2._______________________________________________________
3. So, Pi is an irrational number

22. Activity
c. 2.5 is not a complex number.
1.________________________________________________________
2.________________________________________________________
3. So, 2.5 is not a complex number.

23. Activity
d. Evaporation is not a chemical change
1.________________________________________________________
2.________________________________________________________
3. Therefore, Evaporation is not a chemical change.

24. Activity
e. Gold is a metal
1.________________________________________________________
2.________________________________________________________
3. Therefore, Gold is a metal.

25. Summary
• An argument is an attempt to prove that a statement is correct.
• An argument is composed of premise/s and the conclusion.
• An inductive argument is constructed in such a way that if the
premises are true, then it is highly unlikely that the conclusion is false.

26. Summary
• A deductive argument is so constructed in a way that if the premises
are true, then there is no way that the conclusion is false.
• A valid argument is an argument that follows the correct format.
• A sound argument is an argument that is both a.) valid; and b.) the
premises are correct.

27. Online Quiz
Check the google classroom link. Make sure to finish the assessment
before the deadline.