dichotomy

Noun

dichotomy (countable and uncountable, plural dichotomies)

1. A separation or division into two; a distinction that results in such a division.
   • The dichotomy between the private and the public is central to almost two centuries of feminist writing and political struggle; it is, ultimately, what the feminist movement is all about. Although some feminists treat the dichotomy as a universal, trans-historical and trans-cultural feature of...1989, Carole Pateman, 6: Feminist Critiques of the Public/Private Dichotomy: The Disorder of Women: Democracy, Feminism, and Political Theory, page 118
   • The dichotomy between maria and highlands dominates lunar mineralogy.2003, Thérèse Encrenaz et al., “The Solar System”, in Storm Dunlop, transl., Système Solaire, page 232

   Synonyms:

   bisection

2. Such a division involving apparently incompatible or opposite principles; a duality.
   • But we do not try to characterize the top and bottom parts of the brain in terms of a simple dichotomy or set of dichotomies, which was exactly what was done with the existing and well-known division of the brain into two halves: namely the left versus the right, the dominant pop-culture brain...2013 November 11, Stephen M. Kosslyn, G. Wayne Miller, “How the Brain Creates Personality: A New Theory”, in The Atlantic
3. The division of a class into two disjoint subclasses that are together comprehensive, as the division of human into female and male.
   • But in the fallacy of false dichotomy, not only do the two alternatives fail to be jointly exhaustive, but they are not even likely. As a result, the disjunctive premise is false, or at least probably false.2011, Patrick J. Hurley, A Concise Introduction to Logic, page 162
   • One can ask if for any algebra the considered problem is always in P or NP-complete (P or coNP-complete)? For example, the problem of the satisfiability of a system of polynomial equations over a group G is in P if G is abelian and NP-complete otherwise ([7, 13]).
     One of the most widely known...2011, Tomasz A. Gorarzd, Jacek Krzaczkowski, The Complexity of Problems Connected with Two-Element Algebras, Paweł M. Idziak, Andrzej Wronski, Reports on Mathematical Logic: No. 46, page 92
4. The division of a genus into two species; a division into two subordinate parts.

   Synonyms:

   partition, trichotomy

5. A phase of the moon when it appears half lit and half dark, for example at the quadratures.
   • The Ides of Januarius indeed, the preceding month, must have fallen on March 1 at midnight, two days before the first dichotomy of the mean new moon of that month, March 3 at midnight.1854, Edward Greswell, Origines Kalendariæ Italicæ: Tables of the Roman Calendar, volume 1, page 261
6. Division and subdivision; bifurcation, such as that of a stem of a plant or a vein of the body into two parts as it proceeds from its origin; often successive.
   • In one forked leaf there is a distinct vein dichotomy, and the leaf boundary commences 1.5 mm above the dichotomy.1969, J. F. Rigby, Permian Sphenopsids from Antarctica, Geological Survey Professional Paper 613-F, page F-9
   • In most of the creeping species with dorsiventral stems (e.g., S. kraussiana, S. laevigata) roots arise at or close to the point of dichotomy; in species like S. rupestris and S. wallichii they arise at the point of dichotomy as well as other positions and in S. selaginoides and S. spinulosa they...2010, V. Singh, P. C. Pande, D. K. Jain, Text Book Of Botany: Diversity Of Microbes And Cryptogams, 4th edition, page 511