Case-based reasoning is a problem-solving method in which one develops a solution to a new problem based on past experiences with a different problem. In some cases, one may be able to completely reuse a particular solution, while in other cases the old problem provides only limited insight into the new solution. Case-based reasoning is strongly based in analogy, as individuals look to the past to find situations and problems analogous to the ones that they face in the present. It is highly relevant to the study of human decision making and to computer reasoning technology. Many researchers in the area of human decision making and problem solving believe that nearly all reasoned decisions are made from case-based reasoning.
One can apply case-based reasoning in a variety of different ways based on one's needs in a given situation. A solution to an older problem can be reused to solve a new and analogous problem or can at least suggest a method for solving the new problem. One can use such reasoning to modify a solution to the new problem that doesn't quite work right or to predict potential issues with a new solution. After coming up with a solution to the new problem, one can use analogous past situations to analyze the new solution in order to determine why it worked and to look for potential shortcomings.
Four primary steps characterize case-based reasoning. When a new problem is identified, one must first recall similar past problems. Upon recalling past problems, one reuses a solution or adapts it to the new situation. After this, one must test the new solution to see if it works for the new problem just as it worked for the analogous older problem and must revise the new solution accordingly. Lastly, after finding a working solution, one commits the new problem and solution to memory as a new "case" to which to refer in later instances of case-based reasoning.
Almost all people tend to use case-based reasoning to solve a wide range of problems in their day-to-day lives. Some professions in particular demand frequent use of such reasoning methods. Lawyers and judges, for instance, often base their arguments and decisions on previous similar legal cases. Mathematicians and students of mathematics use case-based reasoning when solving new and unfamiliar math problems. Almost all careers that require problem solving will require the use of such methods of reasoning at some point.