Principle vs. Theory — What's the Difference?
By Tayyaba Rehman & Fiza Rafique — Updated on September 14, 2023
A principle is a fundamental truth or law that serves as the basis for reasoning or action, while a theory is a system of ideas intended to explain observed phenomena. The two are distinct: principles guide action or thought, theories explain or predict.
Difference Between Principle and Theory
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Key Differences
A principle is an essential or foundational rule, law, or truth that serves as the basis for a system of belief, reasoning, or behavior. Theory, in contrast, refers to a coherent group of propositions that seek to explain or interpret facts or phenomena. While a principle provides a normative guideline for action or thought, a theory provides a framework for understanding why things happen as they do.
In science, a principle might be a fundamental law like Newton's First Law of Motion, which offers an axiom from which other conclusions can be drawn. A theory, like the Theory of Evolution, is a well-substantiated explanation that accounts for a body of evidence and stands up to repeated testing and scrutiny. In other words, while principles offer foundational truths, theories seek to explain complex systems or phenomena based on evidence.
From a grammatical standpoint, both "principle" and "theory" are nouns. They can be made plural, as in "principles" and "theories," and they can both serve as the subject or object in a sentence. However, "principle" is more often used in an attributive sense to modify other nouns, such as in "principle component," whereas "theory" is more frequently standalone.
Both principle and theory are often confused or used interchangeably, which can lead to misunderstandings. While principles often find application in ethical and moral frameworks, serving as guidelines for what is considered "right," theories are more about providing explanatory frameworks for understanding the world. Theory often incorporates multiple principles to provide a more complex explanation.
Comparison Chart
Definition
Fundamental truth or law
System of ideas to explain phenomena
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Field of Application
Ethics, law, science
Mainly science
Grammatical Category
Noun
Noun
Plural Form
Principles
Theories
Common Modifiers
Basic, fundamental, ethical
Scientific, theoretical
Compare with Definitions
Principle
A fundamental truth guiding action or belief.
Honesty is a vital principle in any relationship.
Theory
A system of ideas explaining a phenomenon.
Einstein's theory of relativity changed physics.
Principle
A law or rule forming the basis of a physical theory.
The principle of relativity transformed our understanding of space and time.
Theory
A proposed explanation intended to address a problem.
The detective's theory about the crime seemed plausible.
Principle
A moral or ethical standard.
She refused the deal on principle.
Theory
A set of principles forming a basis for action.
Game theory is used to model strategic interactions.
Principle
An accepted or professed rule of action or conduct.
The principle of innocent until proven guilty is essential in legal systems.
Theory
A supposition or assumption used for the sake of argument.
For the sake of theory, let's assume all variables are constant.
Principle
A basic source or element.
Water is a principle component of the human body.
Theory
A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research.
Principle
A principle is a proposition or value that is a guide for behavior or evaluation. In law, it is a rule that has to be or usually is to be followed.
Theory
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.
Principle
A fundamental truth or proposition that serves as the foundation for a system of belief or behaviour or for a chain of reasoning
The basic principles of justice
Theory
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.
Principle
A general scientific theorem or law that has numerous special applications across a wide field.
Theory
A set of theorems that constitute a systematic view of a branch of mathematics.
Principle
A fundamental source or basis of something
The first principle of all things was water
Theory
Abstract reasoning; speculation
A decision based on experience rather than theory.
Principle
A basic truth, law, or assumption
The principles of democracy.
Theory
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.
Principle
A rule or standard, especially of good behavior
A man of principle.
Theory
An assumption based on limited information or knowledge; a conjecture.
Principle
The collectivity of moral or ethical standards or judgments
A decision based on principle rather than expediency.
Theory
A description of an event or system that is considered to be accurate.
Principle
A fixed or predetermined policy or mode of action.
Theory
(sciences) A coherent statement or set of ideas that explains observed facts or phenomena and correctly predicts new facts or phenomena not previously observed, or which sets out the laws and principles of something known or observed; a hypothesis confirmed by observation, experiment etc.
Principle
A basic or essential quality or element determining intrinsic nature or characteristic behavior
The principle of self-preservation.
Theory
(uncountable) The underlying principles or methods of a given technical skill, art etc., as opposed to its practice.
Principle
A rule or law concerning the functioning of natural phenomena or mechanical processes
The principle of jet propulsion.
Theory
(mathematics) A field of study attempting to exhaustively describe a particular class of constructs.
Knot theory classifies the mappings of a circle into 3-space.
Principle
(Chemistry) One of the elements that compose a substance, especially one that gives some special quality or effect.
Theory
A hypothesis or conjecture.
Principle
A basic source. See Usage Note at principal.
Theory
A set of axioms together with all statements derivable from them; or, a set of statements which are deductively closed. Equivalently, a formal language plus a set of axioms (from which can then be derived theorems). The statements may be required to all be bound (i.e., to have no free variables).
A theory is consistent if it has a model.
Principle
A fundamental assumption or guiding belief.
We need some sort of principles to reason from.
Theory
A doctrine, or scheme of things, which terminates in speculation or contemplation, without a view to practice; hypothesis; speculation.
Principle
A rule used to choose among solutions to a problem.
The principle of least privilege holds that a process should only receive the permissions it needs.
Theory
An exposition of the general or abstract principles of any science; as, the theory of music.
Principle
Moral rule or aspect.
I don't doubt your principles.
You are clearly a person of principle.
It's the principle of the thing; I won't do business with someone I can't trust.
Theory
The science, as distinguished from the art; as, the theory and practice of medicine.
Principle
(physics) A rule or law of nature, or the basic idea on how the laws of nature are applied.
Bernoulli's Principle
The Pauli Exclusion Principle prevents two fermions from occupying the same state.
The principle of the internal combustion engine
Theory
The philosophical explanation of phenomena, either physical or moral; as, Lavoisier's theory of combustion; Adam Smith's theory of moral sentiments.
Principle
A fundamental essence, particularly one producing a given quality.
Many believe that life is the result of some vital principle.
Theory
A well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena;
Theories can incorporate facts and laws and tested hypotheses
True in fact and theory
Principle
A source, or origin; that from which anything proceeds; fundamental substance or energy; primordial substance; ultimate element, or cause.
Theory
A tentative theory about the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena;
A scientific hypothesis that survives experimental testing becomes a scientific theory
He proposed a fresh theory of alkalis that later was accepted in chemical practices
Principle
An original faculty or endowment.
Theory
A belief that can guide behavior;
The architect has a theory that more is less
They killed him on the theory that dead men tell no tales
Principle
(obsolete) A beginning.
Theory
A formulation of apparent relationships among certain observed phenomena.
Darwin's theory of evolution is based on natural selection.
Principle
(transitive) To equip with principles; to establish, or fix, in certain principles; to impress with any tenet or rule of conduct.
Principle
Beginning; commencement.
Doubting sad end of principle unsound.
Principle
A source, or origin; that from which anything proceeds; fundamental substance or energy; primordial substance; ultimate element, or cause.
The soul of man is an active principle.
Principle
An original faculty or endowment.
Nature in your principles hath set [benignity].
Those active principles whose direct and ultimate object is the communication either of enjoyment or suffering.
Principle
A fundamental truth; a comprehensive law or doctrine, from which others are derived, or on which others are founded; a general truth; an elementary proposition; a maxim; an axiom; a postulate.
Therefore, leaving the principles of the doctrine of Christ, let us go on unto perfection.
A good principle, not rightly understood, may prove as hurtful as a bad.
Principle
A settled rule of action; a governing law of conduct; an opinion or belief which exercises a directing influence on the life and behavior; a rule (usually, a right rule) of conduct consistently directing one's actions; as, a person of no principle.
All kinds of dishonesty destroy our pretenses to an honest principle of mind.
Principle
Any original inherent constituent which characterizes a substance, or gives it its essential properties, and which can usually be separated by analysis; - applied especially to drugs, plant extracts, etc.
Cathartine is the bitter, purgative principle of senna.
Principle
To equip with principles; to establish, or fix, in certain principles; to impress with any tenet, or rule of conduct, good or ill.
Governors should be well principled.
Let an enthusiast be principled that he or his teacher is inspired.
Principle
A basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct;
Their principles of composition characterized all their works
Principle
A rule or standard especially of good behavior;
A man of principle
He will not violate his principles
Principle
A basic truth or law or assumption;
The principles of democracy
Principle
A rule or law concerning a natural phenomenon or the function of a complex system;
The principle of the conservation of mass
The principle of jet propulsion
The right-hand rule for inductive fields
Principle
Rule of personal conduct
Principle
(law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature);
The rationale for capital punishment
The principles of internal-combustion engines
Common Curiosities
Are principles and theories the same?
No, principles guide action or establish a base, while theories explain or predict.
Are principles scientific?
Principles can be scientific, like Newton's laws, or ethical, like honesty.
How do you pluralize theory?
The plural form is "theories."
How do you pluralize principle?
The plural form is "principles."
Do principles have evidence?
Principles are generally accepted truths and may not require empirical evidence.
Can a theory become a principle?
No, theories explain phenomena while principles serve as foundational truths.
Are theories proven facts?
Theories are well-supported by evidence but are open to revision or falsification.
What is a principle?
A principle is a fundamental truth or law that guides action or thought.
What is a theory?
A theory is a system of ideas meant to explain or interpret observed phenomena.
Is principle a noun?
Yes, "principle" is a noun.
Do theories have evidence?
Yes, theories should be backed by substantial evidence.
Is theory a noun?
Yes, "theory" is also a noun.
Can theories incorporate principles?
Yes, theories often include multiple principles to provide a complex explanation.
Can principle be used in science?
Yes, many scientific laws are often referred to as principles.
Is theory limited to science?
While commonly scientific, theories can exist in other fields like economics.
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Written by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
Co-written by
Fiza RafiqueFiza Rafique is a skilled content writer at AskDifference.com, where she meticulously refines and enhances written pieces. Drawing from her vast editorial expertise, Fiza ensures clarity, accuracy, and precision in every article. Passionate about language, she continually seeks to elevate the quality of content for readers worldwide.
