What is "circumscription"

Circumscription \Cir`cum*scrip"tion\, n. [L. circumscriptio. See Circumscribe.]

1. An inscription written around anything. [R.]
   --Ashmole.

2. The exterior line which determines the form or magnitude of a body; outline; periphery.
   --Ray.

3. The act of limiting, or the state of being limited, by conditions or restraints; bound; confinement; limit.

   The circumscriptions of terrestrial nature.
   --Johnson.

   I would not my unhoused, free condition Put into circumscription and confine.
   --Shak.

1530s, from Latin circumscriptionem (nominative circumscriptio) "an encircling; fact of being held to set limits," noun of action from past participle stem of circumscribere (see circumscribe). Figurative sense of "setting limits of meaning" is earliest in English.

n. 1 the act of circumscribe or the quality of being circumscribed 2 anything that circumscribes or a circumscribed area 3 (context taxonomy English) the definition of what does and does not belong to a given taxon, from a particular taxonomic viewpoint or taxonomic system. 4 An electoral district; used often in texts treating electoral systems in Romance countries.

n. the act of circumscribing

Circumscription is a non-monotonic logic created by John McCarthy to formalize the common sense assumption that things are as expected unless otherwise specified. Circumscription was later used by McCarthy in an attempt to solve the frame problem. To implement circumscription in his initial formulation, McCarthy augmented first-order logic to allow the minimization of the extension of some predicates, where the extension of a predicate is the set of tuples of values the predicate is true on. This minimization is similar to the closed world assumption that what is not known to be true is false.

The original problem considered by McCarthy was that of missionaries and cannibals: there are three missionaries and three cannibals on one bank of a river; they have to cross the river using a boat that can only take two, with the additional constraint that cannibals must never outnumber the missionaries on either bank (as otherwise the missionaries would be killed and, presumably, eaten). The problem considered by McCarthy was not that of finding a sequence of steps to reach the goal (the article on the missionaries and cannibals problem contains one such solution), but rather that of excluding conditions that are not explicitly stated. For example, the solution “go half a mile south and cross the river on the bridge” is intuitively not valid because the statement of the problem does not mention such a bridge. On the other hand, the existence of this bridge is not excluded by the statement of the problem either. That the bridge does not exist is a consequence of the implicit assumption that the statement of the problem contains everything that is relevant to its solution. Explicitly stating that a bridge does not exist is not a solution to this problem, as there are many other exceptional conditions that should be excluded (such as the presence of a rope for fastening the cannibals, the presence of a larger boat nearby, etc.)

Circumscription was later used by McCarthy to formalize the implicit assumption of inertia: things do not change unless otherwise specified. Circumscription seemed to be useful to avoid specifying that conditions are not changed by all actions except those explicitly known to change them; this is known as the frame problem. However, the solution proposed by McCarthy was later shown leading to wrong results in some cases, like in the Yale shooting problem scenario. Other solutions to the frame problem that correctly formalize the Yale shooting problem exist; some use circumscription but in a different way.

Circumscription may refer to:

• Circumscribed circle
• Circumscription (logic)
• Circumscription (taxonomy)
• Carneiro's Circumscription Theory a theory about the origins of the political state in the history of human evolution proposed by the American anthropologist Robert Carneiro.
• Electoral district

In biological taxonomy, circumscription is the definition of a taxon, that is, a group of organisms. For every taxon, the circumscription is based on a set of attributes that characterise every member of the taxon, and exclude every other organism.

One goal of biological taxonomy is to achieve a stable circumscription for every taxon. Achieving stability is not yet a certainty in most taxa, and many that had been regarded as stable for decades are in upheaval in the light of rapid developments in molecular phylogenetics. In essence, new discoveries may invalidate the application of irrelevant attributes used in established or obsolete circumscriptions, or present new attributes useful in cladistic taxonomy.

An example of a taxonomic group with unstable circumscription is Anacardiaceae, a family of flowering plants. Some experts favor a circumscription in which this family includes the Blepharocaryaceae, Julianaceae, and Podoaceae, which are sometimes considered to be separate families.