An Introduction to Reasoning: Inductive versus Deductive Reasoning

An Introduction to Reasoning:

Induction versus Deduction

• The process of induction:
  • Begin with some data , and then determine what general conclusion(s) can logically be derived from that data. 
    • In short, you determine what theory or theories could explain the data.

Induction- A Caution

Consider this example:

•  You note that the probability of becoming diabetes is greatly increased if at least one parent is diabetes, and from that you conclude that diabetes may be inherited . 
  • That is certainly a reasonable hypothesis given the data. However, induction does not prove that the theory is correct. 
• There are often alternative theories that are also supported by the data.
  • For example, the behavior of the diabetic parent may cause the child to be diabetic, not the genes.

• It is important to remember that with induction the theory does indeed offer a logical explanation of the data. 
  • To conclude that the parents have no effect on the children's diabetes is not supportable given the data, and would not be a logical conclusion.

Induction- Examples

• This cat is black. That cat is black A third cat is black. Therefore, all cats are are black.
• This marble from the bag is blue. That marble from the bag is blue. A third marble from the bag is blue. Therefore, all the marbles in the bag blue.

Deduction

• The process of deduction:
  • Begin with some statements, called 'premises', that are assumed to be true.
  • Then determine what else would have to be true if the premises are true. 
    

Deduction- Continued

• With deduction you can provide proof of your conclusions.
  • This is only true if your premises are correct. 
• The premises themselves, however, remain unproven and unprovable, they must be accepted on face value, or by faith, or for the purpose of exploration.

Deduction- Example

All men are mortal . Joe is a man. Therefore, Joe is mortal.

In Conclusion

Deduction and induction by themselves are inadequate to make a compelling argument.

• Deduction gives absolute proof, it never makes contact with the real world; there is no place for observation or experimentation, no way to test the validity of the premises. 
• While induction is driven by observation, it never approaches actual proof of a theory. 

Therefore an effective paper will include both types of logic