Our knowledge of the world is built step by step, through exercising of our reasoning powers. The raw data that we receive through our senses is processed by our mind to create a coherent picture of the world. To make sense of the information that we receive and to understand the working of the world, we need logic and reasoning, which can help us see the bigger picture and complete the jigsaw puzzle of the world picture that we have. Deductive and inductive reasoning are two methods of thought or argumentation, which can help us in our quest of truth.
Reasoning to uncover truth is about making connections between scattered facts to create a theory which explains reality. There are more than one ways of arriving at the truth, by taking different roads of thought. The scientific method is a set of methodologies aimed at discovering the natural laws that give rise to the beautiful structure of the world. Two ways of analyzing reality are going by deductive and inductive reasoning. Let us see what these two approaches are and how are they different from each other.
Differences Between Deductive and Inductive Reasoning
If you know geometry and have worked through all of its theorems and proofs, you have already used deductive logic and if you have engaged in speculative reasoning, you have used inductive logic. Let us see how these two approaches are conceptually different.
Deductive logic or reasoning is an axiomatic approach to thinking about things. You start from some general principles which are known to be true or assumed to be true and then apply these axiomatic principles to more specific cases. It is like constructing a building, where you place solid foundations, over which higher stories are built.
As long as the foundations are strong, the whole logical structure built on the basic premises is bound to be true. That is deductive logic for you. In mathematics and theoretical physics, deductive logic is used to solve problems. From the basic premise of Newton's laws of gravitation and motion, physicists can determine the orbits of planets around the Sun and satellites around the Earth, through deductive logic. Check out some deductive reasoning examples.
Inductive Reasoning, on the other hand, doesn't start with any axiomatic principles. It is a system of thought, designed to arrive at the greater generalizations, from very specific cases, which is a directly inverse approach to deductive logic. An inductive logician tries to 'guess' at what the universal laws are, from very specific cases he sees. The experimentalists and theorists of any field like physics, chemistry, and biology employ inductive logic to arrive at basic laws of nature.
Deductive Vs. Inductive Reasoning: Pros and Cons
Since we don't know all the fundamental laws of nature, a deductive approach is not feasible most of the time. We need to guess or imagine what the true laws could be, from the patterns we see in nature. That's why inductive logic works in science, where it can supply scientists with testable hypotheses which can explain any phenomenon under study.
After checking out some actual reasoning examples, you will realize that while the former is a more solid and infallible approach, which can never lead you astray, it is also a 'closed' logical system which limits the possibilities of thought by the axioms it starts with. For example, Euclidean Geometry, based on basic axioms of flat space cannot explain curved space geometry.
On the other hand, the latter option of inductive thought could lead you astray, but it's open to a lot more possibilities, as there are no restricting axioms. It is a more flexible approach, which is ideal for problem solving. With an inductive reasoning approach, you have more than one hypotheses to be true, which makes it the ideal method of thought for research in fields, where nothing much is known.
While deductive reasoning is a more surefooted approach that is going to ensure that the inferences you arrive at are always going to be true, as long as the basic premises are true, inductive reasoning has the ability to challenge established thought, by arriving at paradigm-shifting generalizations from specific instances; albeit, with the possibility of going wrong. Both approaches have their merits and demerits and we need both, to be able to arrive at the greater truth.