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 [the´ah-re, thēr´e]
1. the doctrine or the principles underlying an art as distinguished from the practice of that particular art.
2. a formulated hypothesis or, loosely speaking, any hypothesis or opinion not based upon actual knowledge.
3. a provisional statement or set of explanatory propositions that purports to account for or characterize some phenomenon. The concepts and provisions set forth in a theory are more specific and concrete than those of a conceptual model. Hence a theory is derived from a conceptual model to fully describe, explain, and predict phenomena within the domain of the model.
attribution theory a theory developed in an attempt to understand why an event occurred so that later events can be predicted and controlled.
care-based theory a type of ethical theory of health care based on the two central constructive ideas of mutual interdependence and emotional response. The ethics of care is a rejection of impartial, principle-driven, dispassionate reasoning and judgment that has often dominated the models and paradigms of bioethics. Its origins are developmental psychology, moral theory, and feminist writings. Its moral concern is with needs and corresponding responsibility as they arise within a relationship. Moral response is individualized and is guided by the private norms of friendship, love, and care rather than by abstract rights and principles.
cell theory all organic matter consists of cells, and cell activity is the essential process of life.
clonal-selection theory of immunity immunologic specificity is preformed during embryonic life and mediated through cell clones.
Cohnheim's theory tumors develop from embryonic rests that do not participate in the formation of normal surrounding tissue.
community-based theory any ethical theory of health care according to which everything fundamental in ethics derives from communal values, the common good, social goals, traditional practices, and cooperative virtues. Commitment is to the general welfare, to common purposes, and to education of community members. Beliefs and principles, shared goals, and obligations are seen as products of the communal life. Conventions, traditions, and social solidarity play a prominent role in this type of theory. Called also communitarianism.
consequence-based theory teleological theory.
continuity theory a theory of motor development that postulates that motor changes occur in a linear fashion during an individual's life and that each change is dependent on the development of the prior period.
deontological theory a type of ethical theory that maintains that some features of actions other than or in addition to consequences make the actions right or wrong. A major postulate is that we may not use or mistreat other people as a means to our own happiness or to that of others. Deontological theories guide action with a set of moral principles or moral rules, but it is the actions themselves and their moral properties that are fundamental. This theory is sometimes called the Kantian theory because the work of Immanuel Kant (1724–1804) has a deep effect on its formulations.
discontinuity theory each stage of motor development has a new and unique feature that is added to distinguish it from the previous stage.
family systems theory a view of the family as a dynamic, interactive unit that undergoes continual evolvement in structure and function. There are subsystems that are discrete units (such as mother-father, sister-brother, and mother-child) and there is a suprasystem (the community). The main functions of the family are considered to be support, regulation, nurturance, and socialization; specific aspects of the functions change as the subsystems interact with the suprasystem.
feminist theory a type of ethical theory whose core assumptions are that women's experiences have not been taken as seriously as men's experiences and that there is subordination of women, which must end. A central theme is that women's reality is a social construction and not a biological determination. See also feminist praxis.
gate theory (gate-control theory) neural impulses generated by noxious painful stimuli and transmitted to the spinal cord by small-diameter C-fibers and A-delta fibers are blocked at their synapses in the dorsal horn by the simultaneous stimulation of large-diameter myelinated A-fibers, thus inhibiting pain by preventing pain impulses from reaching higher levels of the central nervous system.
The gate-control theory of pain. From Linton et al., 2000.
general systems theory a theory of organization proposed by Ludwig von Bertalanffy in the 1950s as a means by which various disciplines could communicate with one another and duplication of efforts among scientists could be avoided. The theory sought universally applicable principles and laws that would hold true regardless of the kind of system under study, the nature of its components, or the interrelationships among its components. Since the introduction of the general systems theory, theoretical models, principles, and laws have been developed that are of great value to scientists in all fields, including those of medicine, nursing, and other health-related professions.
germ theory
1. all organisms are developed from a cell.
2. infectious diseases are of microbial origin.
theory of human becoming a theory of nursing formulated by Rosemarie Rizzo parse. Principles of Martha Rogers' science of unitary human beings are synthesized with major tenets and concepts from existential phenomenological thought to create a conceptual system and theory. Major areas of focus, rooted in the human sciences, describe the unitary human being interrelating with the universe in co-creating health. Essential concepts include the human-universe-health interrelationship, the co-creating of health, and the freely choosing of meaning in becoming. Humans are unitary beings mutually co-creating rhythmical patterns of relating in open interchange with the universe. The human being is a unity of the subject-world relationship, participating with the world in co-creation of self.

Health, in this theory, is a continuously changing process that humans participate in co-creating. Health is human becoming. It is not the opposite of disease, nor is it a state that exists. Disease is viewed as a pattern of the human being's interrelationship with the world.

Nursing is both science and art. The science is nursing's abstract body of knowledge lived through the art in service to people. Three principles of this theory comprise the abstract knowledge base used to guide nursing research and practice. The principles of structuring meaning multidimensionally, co-creating rhythmical patterns of relating, and co-transcending with the possibles provide the underpinnings for practice and research.

There is a particular nursing practice methodology, the only one that evolves directly from a nursing theory. Parse's practice methodology specifies that the nurse be truly present with the person and family illuminating meaning, synchronizing rhythms, and mobilizing transcendence. Persons choose their own patterns of health, reflective of their values. The nurse is there with the person and family as they uncover meanings and make decisions about their life situations. True presence is an unconditional love grounded in the belief that individuals know the way.

Parse has also constructed a research methodology congruent with her theory and unique to nursing. Her research methodology offers the researcher the opportunity to study universal lived experiences from the perspective of the people living the experiences. The purpose of her basic research method is to uncover the meaning of lived experiences to enhance the knowledge base of nursing. Parse has contributed to nursing science a theory with congruent practice and research methodologies.
theory of human caring a nursing theory formulated by Jean watson, derived from the values and assumptions of metaphysical, phenomenological-existential, and spiritual conceptual orientations. The primary concepts of the theory, transpersonal human caring and caring transactions, are multidimensional giving and receiving responses between a nurse and another person. Transpersonal human caring implies a special kind of relationship where both the nurse and the other have a high regard for the whole person in a process of being and becoming. Caring transactions provide a coming together in a lived moment, an actual caring occasion that involves choice and action by both the nurse and another.

Person (other) is defined as an experiencing and perceiving “being in the world,” possessing three spheres; mind, body, and soul. Person is also defined as a living growing gestalt with a unique phenomenal field of subjective reality.

The environment includes an objective physical or material world and a spiritual world. Watson defines the world as including all forces in the universe as well as a person's immediate environment. Critical to this definition is the concept of transcendence of the physical world that is bound in time and space, making contact with the emotional and spiritual world by the mind and soul.

Health is more than the absence of disease. Health is unity and harmony within the mind, body, and soul and is related to the congruence between the self as perceived and the self as experienced.

Nursing is defined as a human science and an activity of art, centered on persons and human health-illness experiences. The goal of nursing is to help persons gain a higher level of harmony within the mind, body and soul. Nursing practice is founded on the human-to-human caring process and a commitment to caring as a moral ideal. The activities of nursing are guided by Watson's ten carative factors, which offer a descriptive topology of interventions. The nursing process is incorporated in these carative factors as “creative problem-solving caring process,” a broad approach to nursing that seeks connections and relations rather than separations.
information theory a mathematical theory dealing with messages or signals, the distortion produced by statistical noise, and methods of coding that reduce distortion to the irreducible minimum.
information processing theory a theory of learning that focuses on internal, cognitive processes in which the learner is viewed as a seeker and processor of information.
Kantian theory deontological theory.
Lamarck's theory the theory that acquired characteristics may be inherited.
Metchnikoff theory the theory that harmful elements in the body are attacked by phagocytes, causing inflammation; see also metchnikoff theory.
middle range theory a testable theory that contains a limited number of variables, and is limited in scope as well, yet is of sufficient generality to be useful with a variety of clinical research questions.
nursing theory
1. a framework designed to organize knowledge and explain phenomena in nursing, at a more concrete and specific level than a conceptual model or a metaparadigm.
2. The study and development of theoretical frameworks in nursing.
obligation-based theory deontological theory.
quantum theory radiation and absorption of energy occur in quantities (quanta) that vary in size with the frequency of the radiation.
recapitulation theory ontogeny recapitulates phylogeny; see also recapitulation theory.
rights-based theory a type of ethical theory under which the language of rights provides the basic terminology for ethical and political theory; it maintains that a democratic society must protect individuals and allow all to pursue personal goals. The idea of primacy of rights has been strongly disputed by, for example, utilitarians and Marxists. Individual interests often conflict with communal or institutional interests, as has been seen in efforts to reform the health care system. A prominent rights-based theory is what is known as liberal individualism.
teleological theory a type of ethical theory that takes judgments of the value of the consequences of action as basic. Utilitarianism is the most prominent consequence-based theory; it accepts one and only one basic principle of ethics, the principle of utility, which asserts that we ought always to produce the maximal balance of positive value over negative consequences (or the least possible negative consequence, if only undesirable results can be achieved).
Young-Helmholtz theory the theory that color vision depends on three sets of retinal receptors, corresponding to the colors of red, green, and violet.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


A reasoned explanation of known facts or phenomena that serves as a basis of investigation by which to seek the truth.
See also: hypothesis, postulate.
[G. theōria, a beholding, speculation, theory, fr. theōros, a beholder]
Farlex Partner Medical Dictionary © Farlex 2012


(thē′ə-rē, thîr′ē)
n. pl. theo·ries
1. A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.
2. The branch of a science or art consisting of its explanatory statements, accepted principles, and methods of analysis, as opposed to practice: a fine musician who had never studied theory.
3. A set of theorems that constitute a systematic view of a branch of mathematics.
4. Abstract reasoning; speculation: a decision based on experience rather than theory.
5. A belief or principle that guides action or assists comprehension or judgment: staked out the house on the theory that criminals usually return to the scene of the crime.
6. An assumption based on limited information or knowledge; a conjecture.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A hypothesis or explanation of a phenomenon based on available data Statistics A general statement predicting, explaining, or describing the relationships among a number of constructs
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


A reasoned explanation of known facts or phenomena that serves as a basis of investigation by which to reach the truth.
See also: hypothesis, postulate
[G. theōria, a beholding, speculation, theory, fr. theōros, a beholder]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005


An explanation of the manner in which a phenomenon occurs, has occurred, or will occur.
Bielschowsky's theory See theories of strabismus.
biological-statistical theory Theory of the development of refractive errors, based on the way in which the refractive components of the eye combine. It postulates a high correlation between the normally distributed refractive components to produce emmetropia. A breakdown of this correlation leads to ametropia. This theory depends essentially on hereditary factors. See gene-environment interaction; myopia control; physiological myopia; emmetropization theory; use-abuse theory.
Chavasse's theory See theories of strabismus.
corpuscular theory See Newton's theory.
Donders' theory See theories of strabismus.
Duane's theory See theories of strabismus.
duplicity theory The theory that vision is mediated by two independent photoreceptor systems in the retina: diurnal or photopic vision through the cones when the eyes see details and colours; and nocturnal or scotopic vision through the rods when the eyes see at very low levels of luminance. It can be illustrated when establishing a dark adaptation curve (sensitivity as a function of time), which is preceded by a bright pre-adaptation stimulus. The curve typically has two branches: and initial increase in sensitivity (i.e. lower light threshold) followed by a plateau, due to cone adaptation; then another increase in sensitivity followed by a plateau due to rod adaptation. See photochromatic interval; Purkinje shift; two visual systems theory; photopic vision; scotopic vision.
emission theory See Newton's theory.
emmetropization theory A theory that explains the phenomenon of emmetropization on a biofeedback mechanism, involving cortical and subcortical control of the various components of the eye that contribute to its refractive power.
empiricist theory Theory that certain aspects of behaviour, perception, development of ametropia, etc. depend on environmental experience and learning, and are not inherited. See empiricism; nativist theory.
Fincham's theory Theory of accommodation which attributes the increased convexity of the front surface of the crystalline lens, when accommodating, to the elasticity of the capsule and to the fact that it is thinner in the pupillary area than near the periphery of the lens. See capsule; Helmholtz's of accommodation theory.
first order theory See gaussian theory.
gaussian theory The theory that for tracing paraxial rays through an optical system, that system can be considered as having six cardinal planes: two principal planes, two nodal planes and two focal planes. The mathematical analysis can be carried out by the paraxial equation. Syn. first order theory; paraxial theory. See Newton's formula; paraxial optics; fundamental paraxial equation; paraxial ray.
von Graefe's theory See theories of strabismus.
Helmholtz's theory of accommodation The theory that in accommodation the ciliary muscle contracts, relaxing the tension on the zonule of Zinn while the shape of the crystalline lens changes, resulting in increased convexity, especially of the anterior surface. Fincham's theory complements that of Helmholtz. See accommodation; Fincham's theory; zonule of Zinn.
Helmholtz's theory of colour vision See Young-Helmholtz theory.
Hering's theory of colour vision Theory that colour vision results from the action of three independent mechanisms, each of which is made up of a mutually antagonistic pair of colour sensations: red-green, yellow-blue and white-black. The latter pair is supposed to be responsible for the brightness aspect of the sensation, whereas the former two would be responsible for the coloured aspect of the sensation. Syn. opponent-process theory; tetrachromatic theory. See colour-opponent cells; Young-Helmholtz theory.
van der Hoeve's theory See theories of strabismus.
Huygen's theory 
See wave theory.
Landolt's theory See theories of strabismus.
lattice theory See Maurice's theory.
Luneburg's theory A theory according to which the geometry of the visual space is described by a variable non-euclidean hyperbolic metric.
Mackenzie's theory See theories of strabismus.
Maurice's theory Theory that explains the transparency of the stroma of the cornea. It states that the stromal fibrils, which have a refractive index of about 1.55 in the dry state, are so arranged as to behave as a series of diffraction gratings permitting transmission through the liquid ground substance (refractive index 1.34). The fibrils are the grating elements that are arranged in a hexagonal lattice pattern of equal spacing and with the fibril interval being less than the wavelength of light. The diffraction gratings eliminate scattered light by destructive interference, except for the normally incident light rays. Light beams that are not normal to the cornea are also transmitted to the oblique lattice plane. However, recent work has demonstrated inconsistencies in lattice space and there is some modification to the original postulate of this theory. Syn. lattice theory.
nativist theory Theory that certain aspects of behaviour, perception, development of ametropia, etc. are inherited and independent of environmental experience. See gene-environment interaction; nativism; empiricist theory.
Newton's theory The theory that light consists of minute particles radiated from a light source at a very high velocity. Syn. corpuscular theory; emission theory. See quantum theory; wave theory.
Nordlow's theory See theories of strabismus.
opponent-colour theory See Hering's of colour vision theory.
paraxial theory See gaussian theory.
Parinaud's theory See theories of strabismus.
Planck's theory See quantum theory.
quantum theory Theory that radiant energy consists of intermittent and spasmodic, minute indivisible amounts called quanta (or photons). This is a somewhat modern version of the theory originally proposed by Newton. Syn. Planck's theory. See photon; Newton's theory; wave theory.
Scobee's theory See theories of strabismus.
theory of strabismus See theories of strabismus.
three-component theory See Young- Helmholtz theory.
trichromatic theory See Young-Helmholtz theory.
two visual systems theory The theory that there are two distinct modes of processing visual information: one pertaining to the identification (or 'what' system) and the other to localization (or 'where' system) of visual stimuli. The identification mode is concerned with resolution and pattern vision, and is associated with the foveal and parafoveal regions of the retina. It is subserved by primary cortical mechanisms. The localization mode is concerned with motion and orientation and is subserved by midbrain visual structures. See magnocellular visual system; parvocellular visual system; duplicity theory.
use-abuse theory Theory that attributes the onset of myopia to an adaptation to the use or misuse of the eyes in prolonged close work with the concomitant lag of accommodation and hyperopic defocus. Environmental factors would be the main cause of myopia. See myopia control; biological-statistical theory.
wave theory Theory that light is propagated as continuous waves. This theory was quantified by the Maxwell equations. The wave theory of light can satisfactorily account for the observed facts of reflection, refraction, interference, diffraction and polarization. However, the interchange of energy between radiation and matter, absorption and the photoelectric effect are explained by the quantum theory. Both the wave and quantum theories of light were combined by the concept of quantum mechanics, and light is now considered to consist of quanta travelling in a manner that can be described by a waveform. Syn. Huygens' theory. See photon; quantum theory; wavelength.
Worth's theory See theories of strabismus.
Young-Helmholtz theory The theory that colour vision is due to a combination of the responses of three independent types of retinal receptors whose maximum sensitivities are situated in the blue, green and red regions of the visible spectrum. This theory has been shown to be correct, except that the pigment in the third receptor has a maximum sensitivity in the yellow and not in the red region of the spectrum. Hering's theory of colour vision, which explains phenomena at a level higher than that of the cone receptors, complements this theory. Syn. Helmholtz's theory of colour vision; three components theory; trichromatic theory. See visual pigment; Hering's of colour vision theory.
Table T1 Main characteristics of the photopic and scotopic visual system
photopic visionscotopic vision
type of visiondiurnal (above 10 cd/m2)nocturnal (below 1023cd/m2)
max. receptor densityfovea20º from fovea
photopigment(s) (and max. absorption)long-wave sensitive (560 nm)rhodopsin (507 nm)
middle-wave sensitive (530 nm)
short-wave sensitive (420 nm)
colour visionpresentabsent
light sensitivitylowhigh
dark adaptation:
time to cone thresholdabout 10 min
time to rod threshold
(about 3 log units below)
about 35 min
max. spectral sensitivity555 nm507 nm
spatial resolution (visual acuity)ExcellentPoor
spatial summationpoorexcellent
temporal resolution (critical fusion
temporal summationpoorexcellent
Stiles-Crawford effectpresentabsent
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann


Reasoned explanation of known facts or phenomena that serves as a basis of investigation by which to seek truth.
[G. theōria, a beholding, speculation, theory, fr. theōros, a beholder]
Medical Dictionary for the Dental Professions © Farlex 2012

Patient discussion about theory

Q. I know I’m supposed to drink 8-10 cups of water a day – but I feel it’s too much for me. I try to drink 8 cups a day but I just can’t continue with it long, I just find myself going to the bathroom every 30 minutes. Any idea?

A. when people thought of this genius theory of drinking 10 cups a day they didn’t take in consideration the amount of water we get from our food, the idea that people working construction need more then 8 cups, that people that work in an air conditioned office and don’t tend to move around too much don’t perspire as well as construction workers. They just took the average data- we loose this amount of water, so we need to replace it. You should listen to your body and not to wise guys.

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