Deductive and inductive reasoning are two forms of logic used by scientists, philosophers and social researchers to reach conclusions. In science, the two forms of reasoning can be distinguished from each other based on whether they start from the top and move down or from the bottom and move up. Deduction seeks to test the validity of theories by finding relative data, while induction begins with data and uses observation to form a theory.
Deductive reasoning is top down. It begins with a theory that seeks to explain a phenomenon and uses data to test whether or not that theory is correct. You can test a theory by forming a hypothesis of how an object will behave. For instance, say you have a theory that a box contains only square objects. From this theory, you might create a testable hypothesis: "If I pull an object out of the box, it will be square." If you pull a sphere out of the box, you have determined that your hypothesis is incorrect, and you will need to revise your theory.
Inductive reasoning works from the bottom up. Unlike deductive reasoning, inductive reasoning begins with observing phenomena. You record observations to note any patterns; once they emerge, you can propose a theory that fits all the patterns in the data. For example, if you test the contents of a box by pulling objects from it and notice that for every two square objects you pull out one sphere, you might form a theory that one-third of the objects in the box are spheres.
The difference in deductive and inductive reasoning styles leads to different styles of experimentation. A deductive experiment will seek to confirm a theory through the process of elimination, testing hypotheses that disprove the theory if they are incorrect. For instance, if you theorize that copper burns blue under certain conditions, and the copper burns red instead, you will need to revise or clarify your theory.
On the other hand, you would design an inductive experiment to test an unexplained phenomenon under a series of circumstances to create a working theory. For example, you might burn copper in combination with water, alcohol and manganese and see what type of flame results. If copper burns red with water and alcohol but blue with manganese, you could then devise a theory about how the color that copper burns relates to other compounds in the environment.
Induction and deduction often work as complementary processes. For instance, when approaching an unresearched phenomenon, you may begin with inductive research to begin to get a sense of the data involved and form an initial theory. You can then test this theory using deductive research. If the deductive research proves the theory false, you can conduct further inductive research to explore the failed test and reach a new theory.