Thought experiment in the context of Ship of Theseus

Hilary Whitehall Putnam (/ˈpʌtnəm/; July 31, 1926 – March 13, 2016) was an American philosopher, mathematician, computer scientist, and figure in analytic philosophy in the second half of the 20th century. He contributed to the studies of philosophy of mind, philosophy of language, philosophy of mathematics, and philosophy of science. Outside philosophy, Putnam contributed to mathematics and computer science. Together with Martin Davis he developed the Davis–Putnam algorithm for the Boolean satisfiability problem and he helped demonstrate the unsolvability of Hilbert's tenth problem.

Putnam applied equal scrutiny to his own philosophical positions as to those of others, subjecting each position to rigorous analysis until he exposed its flaws. As a result, he acquired a reputation for frequently changing his positions. In philosophy of mind, Putnam argued against the type-identity of mental and physical states based on his hypothesis of the multiple realizability of the mental, and for the concept of functionalism, an influential theory regarding the mind–body problem. Putnam also originated the computational theory of mind. In philosophy of language, along with Saul Kripke and others, he developed the causal theory of reference, and formulated an original theory of meaning, introducing the notion of semantic externalism based on a thought experiment called Twin Earth.

Jean Buridan (/ˈbjʊərɪdən/; French: [byʁidɑ̃]; Latin: Johannes Buridanus; c. 1301 – c. 1359/62) was an influential 14th‑century French scholastic philosopher.

Buridan taught in the faculty of arts at the University of Paris for his entire career and focused in particular on logic and on the works of Aristotle. Buridan sowed the seeds of the Copernican Revolution in Europe. He developed the concept of impetus, the first step toward the modern concept of inertia and an important development in the history of medieval science. His name is most familiar through the thought experiment known as Buridan's ass, but the thought experiment does not appear in his extant writings.

John Bordley Rawls (/rɔːlz/; February 21, 1921 – November 24, 2002) was an American moral, legal and political philosopher in the modern liberal tradition. Rawls has been described as one of the most influential political philosophers of the 20th century.

In 1990, Will Kymlicka wrote in his introduction to the field that "it is generally accepted that the recent rebirth of normative political philosophy began with the publication of John Rawls's A Theory of Justice in 1971". Rawls's theory of "justice as fairness" recommends equal basic liberties, equality of opportunity, and facilitating the maximum benefit to the least advantaged members of society in any case where inequalities may occur. Rawls's argument for these principles of social justice uses a thought experiment called the "original position", in which people deliberately select what kind of society they would choose to live in if they did not know which social position they would personally occupy. In his later work Political Liberalism (1993), John Rawls addressed the question of how political power can be exercised legitimately in a society where citizens hold diverse and often conflicting moral, religious, and philosophical points of view.

Twin Earth is a thought experiment proposed by philosopher Hilary Putnam in his papers "Meaning and Reference" (1973) and "The Meaning of 'Meaning'" (1975). It is meant to serve as an illustration of his argument for semantic externalism, or the view that the meanings of words are not purely psychological. The Twin Earth thought experiment was one of three examples that Putnam offered in support of semantic externalism, the other two being what he called the Aluminum-Molybdenum case and the Beech-Elm case. Since the publication of these cases, numerous variations on the thought experiment have been proposed by philosophers.

Erwin Rudolf Josef Alexander Schrödinger (/ˈʃroʊdɪŋər/ SHROH-ding-er, German: [ˈʃʁøːdɪŋɐ] ; 12 August 1887 – 4 January 1961), sometimes written as Schroedinger or Schrodinger, was an Austrian–Irish theoretical physicist who developed fundamental results in quantum theory. In particular, he is recognized for devising the Schrödinger equation, an equation that provides a way to calculate the wave function of a system and how it changes dynamically in time. He coined the term "quantum entanglement" in 1935.

In addition, Schrödinger wrote many works on various aspects of physics: statistical mechanics and thermodynamics, physics of dielectrics, color theory, electrodynamics, general relativity, and cosmology, and he made several attempts to construct a unified field theory. In his book, What Is Life?, Schrödinger addressed the problems of genetics, looking at the phenomenon of life from the point of view of physics. He also paid great attention to the philosophical aspects of science, ancient, and oriental philosophical concepts, ethics, and religion. He also wrote on philosophy and theoretical biology. In popular culture, he is best known for his "Schrödinger's cat" thought experiment.

Bellum omnium contra omnes, a Latin phrase meaning "the war of all against all", is the description that Thomas Hobbes gives to human existence in the state-of-nature thought experiment that he conducts in De Cive (1642) and Leviathan (1651). The common modern English usage is a war of "each against all" where war is rare and terms such as "competition" or "struggle" are more common.

Alice and Bob are fictional characters commonly used as placeholders in discussions about cryptographic systems and protocols, and in other science and engineering literature where there are several participants in a thought experiment. The Alice and Bob characters were created by Ron Rivest, Adi Shamir, and Leonard Adleman in their 1978 paper "A Method for Obtaining Digital Signatures and Public-key Cryptosystems". Subsequently, they have become common archetypes in many scientific and engineering fields, such as quantum cryptography, game theory and physics. As the use of Alice and Bob became more widespread, additional characters were added, sometimes with particular meanings. These characters do not have to refer to people; they refer to generic agents which might be different computers or even different programs running on a single computer.

In philosophy, the original position is a hypothetical position from which members of society would consider which principles they would select for the basic structure of their society if they had no knowledge ahead of time regarding the position which they would end up occupying in that society. The idea of having no such knowledge, because everyone is behind a veil of ignorance, represents a thought experiment often associated with the work of the American philosopher John Rawls.

In this "original position", their position behind the "veil of ignorance" prevents everyone from knowing their ethnicity, social status, gender, and (crucially in Rawls's formulation) their or anyone else's ideas of how to lead a good life. Ideally, this would force participants acting rationally to adopt an "initial agreement" on the principles impartially.

In quantum mechanics, Schrödinger's cat is a thought experiment concerning quantum superposition. In the thought experiment, a hypothetical cat in a closed box may be considered to be simultaneously both alive and dead while it is unobserved, as a result of its fate being linked to a random subatomic event that may or may not occur. This experiment, viewed this way, is described as a paradox. This thought experiment was devised by physicist Erwin Schrödinger in 1935 in a discussion with Albert Einstein to illustrate what Schrödinger saw as the problems of Niels Bohr and Werner Heisenberg's philosophical views on quantum mechanics.

In Schrödinger's original formulation, a cat, a flask of poison, and a radioactive source are placed in a sealed box. If an internal radiation monitor such as a Geiger counter detects radioactivity (a single atom decaying), the flask is shattered, releasing the poison, which kills the cat. If no decaying atom triggers the monitor, the cat remains alive. Mathematically, the wave function that describes the contents of the box is a combination, or quantum superposition, of these two possibilities. Yet, when one looks in the box, one sees the cat either alive or dead, not both alive and dead. This poses the question of when exactly quantum superposition ends and reality resolves into one possibility or the other.

Newton's cannonball was a thought experiment Isaac Newton used to hypothesize that the force of gravity was universal, and it was the key force for planetary motion. It appeared in his posthumously published 1728 work De mundi systemate (also published in English as A Treatise of the System of the World).

The mathematical formulations of quantum mechanics are those mathematical formalisms that permit a rigorous description of quantum mechanics. This mathematical formalism uses mainly a part of functional analysis, especially Hilbert spaces, which are a kind of linear space. Such are distinguished from mathematical formalisms for physics theories developed prior to the early 1900s by the use of abstract mathematical structures, such as infinite-dimensional Hilbert spaces (L space mainly), and operators on these spaces. In brief, values of physical observables such as energy and momentum were no longer considered as values of functions on phase space, but as eigenvalues; more precisely as spectral values of linear operators in Hilbert space.

These formulations of quantum mechanics continue to be used today. At the heart of the description are ideas of quantum state and quantum observables, which are radically different from those used in previous models of physical reality. While the mathematics permits calculation of many quantities that can be measured experimentally, there is a definite theoretical limit to values that can be simultaneously measured. This limitation was first elucidated by Heisenberg through a thought experiment, and is represented mathematically in the new formalism by the non-commutativity of operators representing quantum observables.

In philosophy of mind, a philosophical zombie (or "p-zombie") is a being in a thought experiment that is physically identical to a normal human being but does not have conscious experience. For example, if a philosophical zombie were poked with a sharp object, it would not feel any pain, but it would react exactly the way any conscious human would. In other words, the being has full access consciousness, but no phenomenal consciousness.

Philosophical zombie arguments are used against forms of physicalism and in defense of the hard problem of consciousness, which is the problem of accounting in physical terms for subjective, intrinsic, first-person, what-it's-like-ness experiences. Proponents of philosophical zombie arguments, such as the philosopher David Chalmers, argue that since a philosophical zombie is by definition physically identical to a conscious person, even its logical possibility refutes physicalism. This is because it establishes the existence of conscious experience as a further fact. Philosopher Daniel Stoljar points out that zombies need not be utterly without subjective states, and that even a subtle psychological difference between two hypothetically physically identical people, such as how coffee tastes to them, is enough to refute physicalism. Such arguments have been criticized by many philosophers. Some physicalists, such as Daniel Dennett, argue that philosophical zombies are logically incoherent and thus impossible, or that all humans are philosophical zombies; others, such as Christopher Hill, argue that philosophical zombies are coherent but metaphysically impossible.

The knowledge argument (also known as Mary's Room, Mary the Colour Scientist, or Mary the super-scientist) is a philosophical thought experiment proposed by Frank Jackson in his article "Epiphenomenal Qualia" (1982), and extended in "What Mary Didn't Know" (1986).

The experiment describes Mary, a scientist who exists in a black-and-white world where she has extensive access to physical descriptions of color, but no actual perceptual experience of color. Mary has learned everything there is to learn about color, but she has never actually experienced it for herself. The central question of the thought experiment is whether Mary will gain new knowledge when she goes outside of the colorless world and experiences seeing in color.

In epistemology, the Münchhausen trilemma is a thought experiment intended to demonstrate the theoretical impossibility of proving any truth, even in the fields of logic and mathematics, without appealing to accepted assumptions. If it is asked how any given proposition is known to be true, proof in support of that proposition may be provided. Yet that same question can be asked of that supporting proof and any subsequent supporting proof. The Münchhausen trilemma is that there are only three ways of completing a proof:

• The circular argument, in which the proof of some proposition presupposes the truth of that very proposition
• The regressive argument, in which each proof requires a further proof, ad infinitum
• The dogmatic argument, which rests on accepted precepts which are merely asserted rather than defended

The trilemma, then, is having to choose one of three equally unsatisfying options.

Word and Object, philosopher Willard Van Orman Quine's most famous work, expands on ideas in From a Logical Point of View (1953) and reformulates earlier arguments like his attack on the analytic–synthetic distinction from "Two Dogmas of Empiricism". It introduces the thought experiment of radical translation and the related concept of indeterminacy of translation.

Galileo's ship refers to two physics experiments, a thought experiment and an actual experiment, by Galileo Galilei, the 16th- and 17th-century physicist and astronomer. The experiments were created to argue for the idea of a rotating Earth, as opposed to a stationary Earth around which the Sun, planets, and stars rotate.

An argument that was used at the time was that, if the Earth were rotating, there would be detectable effects on the trajectories of projectiles or falling bodies.