 The term  abduction  has been used in related but sometimes different senses. Roughly speaking, abductive reasoning (also called inference to the best explanation, retroduction, and hypothetical, adductive or presumptive reasoning, among many other terms) can be understood as the process through which an agent (or a group of them) looks for an explanation of a surprising observation. Many forms of intellectual tasks, such as medical and fault diagnosis, legal reasoning, natural language understanding, and (last but not least) scientific discovery, belong to this category, thus making abduction one of the most important reasoning processes.