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| Prepared by: Minh Viet Le |
| Caufield School of Information Technology, |
| Faculty of Information Technology, |
| Monash University |
| Date created: October 2007 |
| Last modified date: 19 August 2008 |
Deduction is a process of deriving the consequences of what is assumed. Given the truth of the assumptions, a valid deduction guarantees the truth of the conclusion. In other words, deduction is a process where the conclusion is followed necessarily from the truth of the premises. In general, deductive reasoning applies general principles to reach specific conclusions.
For example:
All men are mortal.
Michael is a man.
Therefore, Michael is mortal.
If the first two statements are true, the conclusion must be true.
In deductive reasoning, the evidence provided must be true before the conclusion can be drawn. Since it is difficult to prove the premises are true before drawing a conclusion, deductive reasoning has little use in the real world.
Abductive reasoning starts from a set of accepted facts and infers to their most likely, or best, explanations.
For example:
All cats chase mouses.
Tom chases mouses.
Therefore, Tom is a cat.
The most direct application of abduction is that of automatically detecting faults in systems. Abduction can be used to derive sets of faults that are likely to be the cause of the problem.
Inductive reasoning is a process of reasoning in which the premises of an argument are believed to support the conclusion but do not ensure it. Alternatively, induction is a process of generalization based on repeated observations. Generally, inductive reasoning examines specific information, perhaps many pieces of specific information, to derive a general principle.
A general format for inductive reasoning can be described as follows.
After observing many times that x and y are occuring together, a rule can be derived as.
For example:
After observing 1000 shopping baskets in a super market, it is found that everytime a customer buys bread they also buy butter.
Therefore, a rule can be derived as.
If bread is found in a shopping basket, butter will also be found.
Analogy is a reasoning method that produces an argument to a problem based on the same reasoning already given to another different problem.
For example:
A person A in one jurisdiction has committed a crime C. The person A has been sentenced to 5 years in prison. A person B in another jurisdiction has also committed the same crime C.
Therefore, by analogy, the person B should be sentenced to 5 years in prison. However, they are not neccessary to be the same.
The analogy reasoning should be considered as one of the support statements for the argument.