'Deduction' vs. 'Induction' vs. 'Abduction'
Do you have to figure out what time you need to leave your house for an appointment? Or are you trying to decide the best choice for lunch? Or are you baffled about why a half-eaten sandwich is on the counter? These situations call for some method of reasoning, and there are three that we use daily: deduction, induction, and abduction.
Deduction is generally defined as "the deriving of a conclusion by reasoning." Its specific meaning in logic is "inference in which the conclusion about particulars follows necessarily from general or universal premises." Simply put, deduction—or the process of deducing—is the formation of a conclusion based on generally accepted statements or facts. It occurs when you are planning out trips, for instance. Say you have a 10 o'clock appointment with the dentist and you know that it takes 30 minutes to drive from your house to the dentist's. From those two facts, you deduce that you will have to leave your house at 9:30, at the latest, to be at the dentist's on time.
Deductive reasoning always follows necessarily from general or universal premises. If a sandwich is defined as "two or more slices of bread or a split roll having a filling in between," and a hot dog is defined as "a frankfurter; especially : a frankfurter heated and served in a long split roll" then one must deduce that any hot dog served in a split roll is a sandwich.
Whereas in deduction the truth of the conclusion is guaranteed by the truth of the statements or facts considered (the hot dog is served in a split roll and a split roll with a filling in the middle is a sandwich), induction is a method of reasoning involving an element of probability. In logic, induction refers specifically to "inference of a generalized conclusion from particular instances." In other words, it means forming a generalization based on what is known or observed. For example, at lunch you observe 4 of your 6 coworkers ordering the same sandwich. From your observation, you then induce that the sandwich is probably good—and you decide to try it yourself. Induction is at play here since your reasoning is based on an observation of a small group, as opposed to universal premises.
The third method of reasoning, abduction, is defined as "a syllogism in which the major premise is evident but the minor premise and therefore the conclusion only probable." Basically, it involves forming a conclusion from the information that is known. A familiar example of abduction is a detective's identification of a criminal by piecing together evidence at a crime scene. In an everyday scenario, you may be puzzled by a half-eaten sandwich on the kitchen counter. Abduction will lead you to the best explanation. Your reasoning might be that your teenage son made the sandwich and then saw that he was late for work. In a rush, he put the sandwich on the counter and left.
If you have trouble differentiating deduction, induction, and abduction, thinking about their roots might help. All three words are based on Latin ducere, meaning "to lead." The prefix de- means "from," and deduction derives from generally accepted statements or facts. The prefix in- means "to" or "toward," and induction leads you to a generalization. The prefix ab- means "away," and you take away the best explanation in abduction.