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Inductive reasoning starts with specific observations and expands them into a general theory, while deductive reasoning starts with a general theory and works towards a specific conclusion. Both can lead to false results if the initial premise is false.
Inductive and deductive reasoning are both approaches that can be used to evaluate inferences. Deductive reasoning involves starting with a general theory or claim, and then moving toward a specific conclusion. Inductive reasoning, on the other hand, takes a number of specific observations and tries to expand them into a more general theory. Each approach is very different and it is important to be aware that both inductive and deductive reasoning can end up with false results, especially if the initial premise of the reasoning is false, in which case the results are termed “invalid”.
Inductive reasoning
A simplistic example of inductive reasoning might start with an observation like “All the cows I’ve seen have been sighted.” One might, in turn, think that therefore all cows must be sighted. This is not actually the case, but given the information available, one could be forgiven for thinking so. The next step in this logic might involve trying to find things that disprove the claim that all cows are sighted, as might be done by asking other people if they have seen any cows that have not been sighted.
Inductive reasoning is commonly seen in the sciences when people want to make sense of a series of observations. Isaac Newton, for example, famously used inductive reasoning to develop a theory of gravity. Using observations, people can develop a theory to explain those observations and seek disproof of that theory. As can be seen in the cow example above, one of the major flaws of inductive reasoning is that it depends on observations, and when observations are incomplete, invalid results can be formulated.
In a famous example of inductive reasoning, some people in the ancient world believed that meat spontaneously gave rise to worms. Their conclusion was based on the observation that if the meat were omitted, the worms would appear. Someone else decided to test this theory by looking for a disprove: would it be possible to leave the meat out and not have the worms appear? By sequestering the meat in various containers alongside the fully exposed meat, the scientist realized that the worms were, in fact, the result of eggs laid by flies.
Deductive reasoning
With deductive reasoning, you take a general theory or idea, test it, and work your way through a sequence of ideas to arrive at a specific conclusion. It is possible to arrive at an unfounded result by using a false initial premise, as in this case: every animal that eats mice is a cat. Rover eats mice. Therefore, Rover is a cat. The goal of deductive reasoning is to arrive at a valid chain of reasoning, in which every statement holds up to testing, but it is possible for deductive reasoning to be valid and invalid.
Both approaches are useful
The brain is so skilled at both deductive and inductive reasoning that it often does so to a degree that people aren’t fully aware of. Especially in the case of children, this type of reasoning is used to make sense of the world and the things observed in it. As you can see, both approaches can be used to explore a logical problem.
