Several extinct species have been postulated, but owing to a lack of evidence they can only be regarded as hypothetical potentially extinct species. They have caused confusion, as they may have been a separate species, a subspecies, an introduced species or a misidentification.

Hypothetical technology is technology that does not exist yet, but that could exist in the future. This article presents examples of technologies that have been hypothesized or proposed, but that have not been developed yet.

<artificial intelligence> (CBR) A technique for problem solving which looks for previous examples which are similar to the current problem. This is useful where heuristic knowledge is not available. There are many situations where experts are not happy to be questioned about their knowledge by people who want to write the knowledge in rules, for use in expert systems. In most of these situations, the natural way for an expert to describe his or her knowledge is through examples, stories or cases (which are all basically the same thing). Such an expert will teach trainees about the expertise by apprenticeship, i.e. by giving examples and by asking the trainees to remember them, copy them and adapt them in solving new problems if they describe situations that are similar to the new problems. CBR aims to exploit such knowledge. Some key research areas are efficient indexing, how to define "similarity" between cases and how to use temporal information. (1996-05-28)