A fact is an occurrence in the real world.  The usual test for a statement of fact is verifiability—that is whether it can be demonstrated to correspond to experience. Standard reference works are often used to check facts. Scientific facts are verified by repeatable careful observation or measurement by experiments or other means.
For example, "This sentence contains words." accurately describes a linguistic fact, and "The sun is a star" accurately describes an astronomical fact. Further, " Abraham Lincoln was the 16th President of the United States" and "Abraham Lincoln was assassinated" both accurately describe historical facts. Generally speaking, facts are independent of belief and of knowledge.
Etymology and usage
The word "fact" derives from the Latin factum, and was first used in English with the same meaning: a thing done or performed a meaning now obsolete.  The common usage of "something that has really occurred or is the case" dates from the middle of the sixteenth century. 
Alternatively, fact may also indicate an allegation or stipulation of something that may or may not be a true fact,  (e.g., "the author's facts are not trustworthy"). This alternate usage, although contested by some, has a long history in standard English. 
Fact may also indicate findings derived through a process of evaluation, including review of testimony, direct observation, or otherwise; as distinguishable from matters of inference or speculation.  This use is reflected in the terms "fact-find" and "fact-finder" (e.g., "set up a fact-finding commission"). 
Facts may be checked by reason, experiment, personal experience, or may be argued from authority. Roger Bacon wrote "If in other sciences we should arrive at certainty without doubt and truth without error, it behooves us to place the foundations of knowledge in mathematics." 
In philosophy, the concept fact is considered in epistemology and ontology. Questions of objectivity and truth are closely associated with questions of fact. A "fact" can be defined as something that is the case—that is, a state of affairs.  
Facts may be understood as information that makes a true sentence true.  Facts may also be understood as those things to which a true sentence refers. The statement "Jupiter is the largest planet in the solar system" is about the fact Jupiter is the largest planet in the solar system. 
Correspondence and the slingshot argument
Pascal Engel's version of the correspondence theory of truth explains that what makes a sentence true is that it corresponds to a fact.  This theory presupposes the existence of an objective world.
The Slingshot argument claims to show that all true statements stand for the same thing—the truth value true. If this argument holds, and facts are taken to be what true statements stand for, then we reach the counter-intuitive conclusion that there is only one fact—the truth. 
Any non-trivial true statement about reality is necessarily an abstraction composed of a complex of objects and properties or relations.  For example, the fact described by the true statement " Paris is the capital city of France" implies that there is such a place as Paris, there is such a place as France, there are such things as capital cities, as well as that France has a government, that the government of France has the power to define its capital city, and that the French government has chosen Paris to be the capital, that there is such a thing as a place or a government, and so on. The verifiable accuracy of all of these assertions, if facts themselves, may coincide to create the fact that Paris is the capital of France.
Difficulties arise, however, in attempting to identify the constituent parts of negative, modal, disjunctive, or moral facts. 
Moral philosophers since David Hume have debated whether values are objective, and thus factual. In A Treatise of Human Nature Hume pointed out there is no obvious way for a series of statements about what ought to be the case to be derived from a series of statements of what is the case. Those who insist there is a logical gulf between facts and values, such that it is fallacious to attempt to derive values from facts, include G. E. Moore, who called attempting to do so the naturalistic fallacy.
Factuality—what has occurred—can also be contrasted with counterfactuality: what might have occurred, but did not. A counterfactual conditional or subjunctive conditional is a conditional (or "if-then") statement indicating what would be the case if events had been other than they were. For example, "If Alexander had lived, his empire would have been greater than Rome." This contrasts with an indicative conditional, which indicates what is (in fact) the case if its antecedent is (in fact) true—for example, "If you drink this, it will make you well."
The definition of a scientific fact is different from the definition of fact, as it implies knowledge. A scientific fact is a repeatable careful observation or measurement (by experimentation or other means), also called empirical evidence. These are central to building scientific theories. Various forms of observation and measurement lead to fundamental questions about the scientific method, and the scope and validity of scientific reasoning.
Various scholars have offered significant refinements to this basic formulation. Philosophers and scientists are careful to distinguish between: 1) states of affairs in the external world and 2) assertions of fact that may be considered relevant in scientific analysis. The term is used in both senses in the philosophy of science. 
Scholars and clinical researchers in both the social and natural sciences have written about numerous questions and theories that arise in the attempt to clarify the fundamental nature of scientific fact.  Pertinent issues raised by this inquiry include:
- the process by which "established fact" becomes recognized and accepted as such; 
- whether and to what extent "fact" and "theoretic explanation" can be considered truly independent and separable from one another;  
- to what extent "facts" are influenced by the mere act of observation;  and
- to what extent factual conclusions are influenced by history and consensus, rather than a strictly systematic methodology. 
Consistent with the idea of confirmation holism, some scholars assert "fact" to be necessarily "theory-laden" to some degree. Thomas Kuhn points out that knowing what facts to measure, and how to measure them, requires the use of other theories. For example, the age of fossils is based on radiometric dating, which is justified by reasoning that radioactive decay follows a Poisson process rather than a Bernoulli process. Similarly, Percy Williams Bridgman is credited with the methodological position known as operationalism, which asserts that all observations are not only influenced, but necessarily defined, by the means and assumptions used to measure them.[ citation needed]
The scientific method
Apart from the fundamental inquiry into the nature of scientific fact, there remain the practical and social considerations of how fact is investigated, established, and substantiated through the proper application of the scientific method.  Scientific facts are generally believed independent of the observer: no matter who performs a scientific experiment, all observers agree on the outcome.  In addition to these considerations, there are the social and institutional measures, such as peer review and accreditation, that are intended to promote factual accuracy (among other interests) in scientific study. 
E. H. Carr in his 1961 volume What is History? argues that the inherent biases from the gathering of facts makes the objective truth of any historical perspective idealistic and impossible. Facts are, "like fish in the Ocean," of which we may only happen to catch a few, only an indication of what is below the surface. Even a dragnet cannot tell us for certain what it would be like to live below the Ocean's surface. Even if we do not discard any facts (or fish) presented, we will always miss the majority; the site of our fishing, the methods undertaken, the weather and even luck play a vital role in what we will catch. Additionally, the composition of history is inevitably made up by the compilation of many different biases of fact finding – all compounded over time. He concludes that for a historian to attempt a more objective method, one must accept that history can only aspire to a conversation of the present with the past – and that one's methods of fact gathering should be openly examined. The set of highlighted historical facts, and their interpretations, therefore changes over time, and reflect present consensuses.
In most common law jurisdictions,  the general concept and analysis of fact reflects fundamental principles of jurisprudence, and is supported by several well-established standards.   Matters of fact have various formal definitions under common law jurisdictions.
- the determinations of the finder of fact after evaluating admissible evidence produced in a trial or hearing; 
- a potential ground of reversible error forwarded on appeal in an appellate court;  and
- any of various matters subject to investigation by official authority to establish whether a crime has been perpetrated, and to establish culpability. 
A party to a civil suit generally must clearly state all relevant allegations of fact that form the basis of a claim. The requisite level of precision and particularity of these allegations varies, depending on the rules of civil procedure and jurisdiction. Parties who face uncertainties regarding facts and circumstances attendant to their side in a dispute may sometimes invoke alternative pleading.  In this situation, a party may plead separate sets of facts that (when considered together) may be contradictory or mutually exclusive. This (seemingly) logically-inconsistent presentation of facts may be necessary as a safeguard against contingencies (such as res judicata) that would otherwise preclude presenting a claim or defense that depends on a particular interpretation of the underlying facts and ruling of the court. 
- Bunge, M. (2003), Philosophical dictionary. Amherst, NY: Prometheus Books, p. 104.
- "Fact". OED_2d_Ed_1989, (but note the conventional uses: after the fact and before the fact).
- "Fact" (1a). OED_2d_Ed_1989 Joye Exp. Dan. xi. Z vij b, Let emprours and kinges know this godly kynges fact. 1545
- "Fact" (6c). OED_2d_Ed_1989
- (See also "Matter" (2,6). Compact_OED)
- "Fact" (5). OED_2d_Ed_1989
- According to the American Heritage Dictionary of the English Language, "Fact has a long history of usage in the sense 'allegation'" AHD_4th_Ed. The OED dates this use to 1729.
- "Fact" (6a). OED_2d_Ed_1989
- "Fact" (8). OED_2d_Ed_1989
- Roger Bacon, translated by Robert Burke Opus Majus, Book I, Chapter 2.
- "A fact, it might be said, is a state of affairs that is the case or obtains." – Stanford Encyclopaedia of Philosophy. States of Affairs
- See Wittgenstein, Tractatus Logico-Philosophicus, Proposition 2: What is the case—a fact—is the existence of states of affairs.
- "A fact is, traditionally, the worldly correlate of a true proposition, a state of affairs whose obtaining makes that proposition true." – Fact in The Oxford Companion to Philosophy
- Alex Oliver, Fact, in Craig, Edward (2005). Shorter Routledge Encyclopedia of Philosophy. Routledge, Oxford. ISBN 0-415-32495-5.
- Engel, Pascal (2002). Truth. McGill-Queen's Press – MQUP. ISBN 0-7735-2462-2.
- The argument is presented in many places, but see for example Davidson, Truth and Meaning, in Davidson, Donald (1984). Truth and Interpretation. Clarendon Press, Oxford. ISBN 0-19-824617-X.
- "Facts possess internal structure, being complexes of objects and properties or relations" Oxford Companion to Philosophy
- Fact, in The Oxford Companion to Philosophy, Ted Honderich, editor. (Oxford, 1995) ISBN 0-19-866132-0
- Gower, Barry (1997). Scientific Method: A Historical and Philosophical Introduction. Routledge. ISBN 0-415-12282-1.
- Ravetz, Jerome Raymond (1996). Scientific Knowledge and Its Social Problems. Transaction Publishers. ISBN 1-56000-851-2.
- (Gower 1996)
- (see e.g., Ravetz, p. 182 fn. 1)
- Ravetz, p. 185
- Gower, p. 138
- Gower, p. 7
- Ravetz p. 181 et. seq. (Chapter Six: "Facts and their evolution")
- Cassell, Eric J. The Nature of Suffering and the Goals of Medicine Oxford University Press. Retrieved 16 May 2007.
- (Ravetz 1996)
- Ed. note: this section of the article emphasizes common law jurisprudence (as primarily represented in Anglo-American–based legal tradition). Nevertheless, the principles described herein have analogous treatment in other legal systems (such as civil law systems) as well.
- Estrich, Willis Albert (1952). American Jurisprudence: A Comprehensive Text Statement of American Case Law. Lawyers Co-operative Publishing Company.
- Elkouri, Frank (2003). How Arbitration Works. BNA Books. p. 305. ISBN 1-57018-335-X.
- Bishin, William R. (1972). Law Language and Ethics: An Introduction to Law and Legal Method. Foundation Press. p. 277. Original from the University of Michigan Digitized 2006.
- The Yale Law Journal: Volume 7. Yale Law Journal Co. 1898.
- Per Lord Shaw of Dunfermline, Clarke v. Edinburgh and District Tramways Co, 1919 S.C.(H.L.) 35, at p 36.
- Merrill, John Houston (1895). The American and English Encyclopedia of Law. E. Thompson. Original from Harvard University Digitized 2007.
- Bennett, Wayne W. (2003). Criminal Investigation. Thomson Wadsworth. ISBN 0-534-61524-4.
- Roy W. McDonald, "Alternative Pleading in the United States". Columbia Law Review, Vol. 52, No. 4 (Apr. 1952), pp. 443–478
- (McDonald 1952)
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