There are three approaches to reasoning: Deductive, Inductive, and Inductive-Deductive.
Aristotle was a proponent of deductive reasoning, and his approach dominated the discourse for several centuries.
Put simply, deductive reasoning is a logical way of arriving at a conclusion. It involves generating a major premise based on either a self-evident or a-priori proposition; a minor premise that provides a specific instance of the major premise; and a conclusion.
For instance, one may logically progress from major premise to a conclusion as under:
Major premise: All birds have wings
Minor premise: The crow is a bird
Conclusion: Therefore the crow has wings
Here, the underlying assumption is that a valid conclusion can be deduced from a valid premise through a sequence of formal steps of logic.
While attractive, this approach has its limitations:
- It can handle certain kinds of statements only
- The validity of the premise depends on the accuracy of the observations behind the premise.
To illustrate the above, let us consider the following:
Major premise: All birds have wings and can fly
Minor premise: The ostrich is a bird
Conclusion: Therefore the ostrich can fly
Clearly, the conclusion is incorrect. The major premise that all birds can fly was incorrect to begin with. However, unless one had observed a flightless bird, it is quite likely that one would base the major premise on known facts- that all birds can fly. Then, if one were asked about a specific bird (that one has not seen), an incorrect conclusion is entirely possible.
As an advancement over experience, and with the requirement of logic to perform deductive reasoning, this approach was popular with teachers and people of learning. However, this popularity waned during the Renaissance.
Among the major criticisms of this approach were:
Major premises were often simply preconceived notions, and the conclusions merely served to confirm pre-existing beliefs.
Logic and authority were considered as conclusive proof. Essentially, if the logic behind a particular conclusion was supported by a large number of authority figures, said conclusion would be considered as conclusively proved. Therefore, over time, people simply went about convincing authorities to accept conclusions as true. This is similar to ‘expert opinion’ in the present time- of very poor evidentiary quality. However, this was what carried weight at the time.