Verisimilitude is the quality of realism in something (such as film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...

, literature
Literature is the art of written works, and is not bound to published sources...

, the arts, etc).

Competing ideas

The problem of verisimilitude is the problem of articulating what it takes for one false theory
The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...

 to be closer to the truth than another false theory. This problem was central to the philosophy of science
Philosophy of science
The philosophy of science is concerned with the assumptions, foundations, methods and implications of science. It is also concerned with the use and merit of science and sometimes overlaps metaphysics and epistemology by exploring whether scientific results are actually a study of truth...

 of Karl Popper
Karl Popper
Sir Karl Raimund Popper, CH FRS FBA was an Austro-British philosopher and a professor at the London School of Economics...

, largely because Popper was among the first to affirm that truth is the aim of scientific
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

 inquiry while acknowledging that most of the greatest scientific theories in the history of science are, strictly speaking, false. If this long string of purportedly false theories is to constitute progress with respect to the goal of truth then it must be at least possible for one false theory to be closer to the truth than others.

Popper assumed that scientists are interested in highly informative theories, in part for methodological reasons — the more informative a theory, the easier it is to test, and the greater its predictive power. But clearly informative power by itself is rather easy to come by, and we do not want to gain content by sacrificing truths. So Popper proposed that closeness to the truth is a function of two factors — truth and content. The more truths that a theory entails (other things being equal) the closer it is to the truth.

Intuitively at least, it seems that Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

's theory of motion entails a good many more truths than does, say, Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

's theory - despite the fact that both are known to be false. Even two true theories can have differing degrees of verisimilitude, depending on how much true information they deliver. For example, the claim that "it will be raining on Thursday next week", if true, is closer to the truth than the true but logically weaker claim that "it will either be raining next Thursday or it will be sunny'".

Popper's formal definition of verisimilitude was challenged, by Pavel Tichý
Pavel Tichý
Pavel Tichý was a Czech logician, philosopher and mathematician.He worked in the field of intensional logic and founded Transparent Intensional Logic, an original theory of the logical analysis of natural languages – the theory is devoted to the problem of saying exactly what it is that we learn,...

  and David Miller
David Miller (philosopher)
David W. Miller is a philosopher and prominent exponent of critical rationalism. He taught in the Department of Philosophy at the University of Warwick in Coventry, UK....

. They argue that they have shown that Popper's definition has the following unintended consequence: that no false theory could be closer to the truth than another. This result gave rise to a search for an account of verisimilitude that did not deem progress towards the truth an impossibility.

Some of the new theories (e.g. Miller, Kuipers) build on Popper's approach, guided by the notion that truthlikeness is a function of a truth factor and a content factor. Others (e.g. Schurz, Weingartner, Mortenson, Gemes) are also inspired by Popper's approach but locate what they believe to be the error of Popper's proposal in his overly generous notion of content, or consequence, proposing instead that the consequences that contribute to closeness to truth must be, in a technical sense, "relevant". A different approach (e.g. Tichý, Hilpinen, Niiniluoto
Ilkka Niiniluoto
Ilkka Maunu Olavi Niiniluoto is a Finnish philosopher and mathematician, serving as a professor of philosophy at the University of Helsinki since 1981. He is currently on leave from his position, having been appointed as rector of the University of Helsinki on August 1, 2003 for a five-year period...

, Oddie) takes the "likeness" in truthlikeness literally, holding that a proposition's likeness to the truth is a function of the overall likeness to the actual world of the possible worlds in which the proposition would be true. There is currently a debate about whether or to what extent these different approaches to the concept are compatible.

Another important problem in Popper's theory of verisimilitude, which is not so deeply discussed in some of the more recent, technical approaches to the question, is the connection between truthlikeness as the goal of scientific progress, on the one hand, and methodology, on the other hand, as the ways in which we can to some extent ensure that scientific research actually approaches this goal. Popper conceived of his definition as a justification of his own preferred methodology: falsificationism, in the following sense: suppose theory A is closer to the truth than theory B according to Popper's qualitative definition of verisimilitude; in this case, we will (or should, if that definition had been logically sound) have that all true consequences of B are consequences of A, and that all false consequences of A are consequences of B; this means that, if A and B are so related, then it should be the case that all known false empirical
Empirical research
Empirical research is a way of gaining knowledge by means of direct and indirect observation or experience. Empirical evidence can be analyzed quantitatively or qualitatively...

consequences of A also follow from B, and all known true empirical consequences of B do follow from A. So, if A were closer to the truth than B, then A should be better corroborated than B by any possible amount of empirical evidence. Lastly, this easy theorem allows to interpret the fact that A is actually better corroborated than B as a corroboration of the hypothesis (or 'meta-hypothesis') that A is more verisimilar than B.

The following question remains: if the goal of science is to find out more and more verisimilar theories, what kind of methods must scientists follow?
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