Deductive Reasoning (‘Top Down’)
Deductive reasoning is a logical process in which a conclusion is based on the concordance of multiple premises that are generally assumed to be true. The eventual knowledge produced depends on which axioms or facts the thinker accepts.
When one reasons deductively, they start with a theory, or general principles and form a conclusion for a specific instance. For example, “all seals are cute; Franco is a seal; therefore Franco is cute”. In many cases, deductive reasoning is also an example of syllogistic reasoning (referred to later).
Deductive reasoning is often very accurate, as long as the initial generalization/theory is true.
Inductive reasoning is a logical process in which multiple premises, all believed true or found true most of the time, are combined to obtain a specific conclusion.
When one reasons inductively, they start with a specific instance, and conclude on a general principle or theory. For example: “Jason has worn black socks to school everyday for the past year; Jason wears black socks everyday and he will wear them today."
Inductive reasoning is not always accurate, because it usually involves generalization. However, generalizations are often necessary.
In the case of language, generalizations are needed so that we don’t treat each experience/object as unique one, and are able to generalize multiple experiences/objects into simple words.
The language that we use is often based on generalizations. At a young age, children will generalize specific objects and feelings into language. For example, a child might see a vehicle and say the word “car”. If the child has generalized correctly, parents will confirm to the child that he or she is correct. If the child has generalized incorrectly, than the parents will correct the child, perhaps saying “No, that’s a truck.”
It is in this way that language is related to reason. It can be argued that language is used to generalize our experiences as individuals. This way, we don’t treat each experience as unique, and are able to generalize multiple experiences into simple words.
A very important concept related to reasoning is the difference between truth and validity.
An argument that is valid is only concerned about pure logic. In other words, does the argument make sense in terms of pure logic.
“Lions eat zebras; a lion ate Dylan; therefore Dylan is a zebra”
Using syllogistic reasoning, this argument makes sense. It is logical. If A eats B, and A eats C, then B is C.
However, this statement, although valid is not necessarily true. Using deductive reasoning, one knows that no human can be a zebra.
This relationship between what is true and what is valid is often explored when discussing reasoning. It is often due to an individual's past experiences that they can rationalize what is true and what is valid.
Here is a great quote on truth vs reason from A.C. Grayling:
"Logic as a science is not the science of truth, but of reasoning; in addition to reason, you need facts; getting the latter, and getting them straight, is a matter of care, common sense, discipline, hard work, and scrupulous enquiry. All these things are beyond the attention span of most, which is why there is so much folly in the world. This is because most reasoning - such as it is - operates not on facts but prejudices and superstitions, and thus it is that people go to war with one another, and spit in each other's eyes." (A.C. Grayling)