List of unsolved problems in philosophy

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This is a list of some of the major unsolved problems in philosophy . Clearly, unsolved philosophical problems exist in the lay sense (e.g. "What is the meaning of life?", "Where did we come from?", "What is reality?", etc.). However, professional philosophers generally accord serious philosophical problems specific names or questions, which indicate a particular method of attack or line of reasoning. As a result, broad and untenable topics become manageable. It would therefore be beyond the scope of this article to categorize "life" (and similar vague categories) as an unsolved philosophical problem.

Philosophy Study of general and fundamental questions

Philosophy is the study of general and fundamental questions about existence, knowledge, values, reason, mind, and language. Such questions are often posed as problems to be studied or resolved. The term was probably coined by Pythagoras. Philosophical methods include questioning, critical discussion, rational argument, and systematic presentation. Classic philosophical questions include: Is it possible to know anything and to prove it? What is most real? Philosophers also pose more practical and concrete questions such as: Is there a best way to live? Is it better to be just or unjust? Do humans have free will?

Meaning of life Philosophical and spiritual question concerning the significance of living or existence in general

The meaning of life, or the answer to the question "What is the meaning of life?", pertains to the significance of living or existence in general. Many other related questions include: "Why are we here?", "What is life all about?", or "What is the purpose of existence?" There have been a large number of proposed answers to these questions from many different cultural and ideological backgrounds. The search for life's meaning has produced much philosophical, scientific, theological, and metaphysical speculation throughout history. Different people and cultures believe different things for the answer to this question.

Reality is the sum or aggregate of all that is real or existent, as opposed to that which is merely imaginary. The term is also used to refer to the ontological status of things, indicating their existence. In physical terms, reality is the totality of the universe, known and unknown. Philosophical questions about the nature of reality or existence or being are considered under the rubric of ontology, which is a major branch of metaphysics in the Western philosophical tradition. Ontological questions also feature in diverse branches of philosophy, including the philosophy of science, philosophy of religion, philosophy of mathematics, and philosophical logic. These include questions about whether only physical objects are real, whether reality is fundamentally immaterial, whether hypothetical unobservable entities posited by scientific theories exist, whether God exists, whether numbers and other abstract objects exist, and whether possible worlds exist.




In art, essentialism is the idea that each medium has its own particular strengths and weaknesses, contingent on its mode of communication. A chase scene, for example, may be appropriate for motion pictures, but poorly realized in poetry, because the essential components of the poetic medium are ill suited to convey the information of a chase scene. This idea may be further refined, and it may be said that the haiku is a poor vehicle for describing a lover's affection, as opposed to the sonnet. Essentialism is attractive to artists, because it not only delineates the role of art and media, but also prescribes a method for evaluating art (quality correlates to the degree of organic form). However, considerable criticism has been leveled at essentialism, which has been unable to formally define organic form or for that matter, medium. What, after all, is the medium of poetry? If it is language, how is this distinct from the medium of prose fiction? Is the distinction really a distinction in medium or genre? Questions about organic form, its definition, and its role in art remain controversial. Generally, working artists accept some form of the concept of organic form, whereas philosophers have tended to regard it as vague and irrelevant.

Film sequence of images that give the impression of movement

A film, also called a movie, motion picture, moving picture, or photoplay, is a series of still images that, when shown on a screen, create the illusion of moving images. This optical illusion causes the audience to perceive continuous motion between separate objects viewed in rapid succession. The process of filmmaking is both an art and an industry. A film is created by photographing actual scenes with a motion-picture camera, by photographing drawings or miniature models using traditional animation techniques, by means of CGI and computer animation, or by a combination of some or all of these techniques, and other visual effects.

Poetry form of literature

Poetry is a form of literature that uses aesthetic and rhythmic qualities of language—such as phonaesthetics, sound symbolism, and metre—to evoke meanings in addition to, or in place of, the prosaic ostensible meaning.

Haiku (俳句)listen  is a very short form of Japanese poetry in three phrases, typically characterized by three qualities:

  1. The essence of haiku is "cutting" (kiru). This is often represented by the juxtaposition of two images or ideas and a kireji between them, a kind of verbal punctuation mark which signals the moment of separation and colours the manner in which the juxtaposed elements are related.
  2. Traditional haiku often consist of 17 on, in three phrases of 5, 7, and 5 on, respectively.
  3. A kigo, usually drawn from a saijiki, an extensive but defined list of such terms.

Art objects

This problem originally arose from the practice rather than theory of art. Marcel Duchamp, in the 20th century, challenged conventional notions of what "art" is, placing ordinary objects in galleries to prove that the context rather than content of an art piece determines what art is. In music, John Cage followed up on Duchamp's ideas, asserting that the term "music" applied simply to the sounds heard within a fixed interval of time.

Marcel Duchamp French painter and sculptor

Henri-Robert-Marcel Duchamp was a French-American painter, sculptor, chess player, and writer whose work is associated with Cubism, Dada, and conceptual art. He was careful about his use of the term Dada and was not directly associated with Dada groups. Duchamp is commonly regarded, along with Pablo Picasso and Henri Matisse, as one of the three artists who helped to define the revolutionary developments in the plastic arts in the opening decades of the 20th century, responsible for significant developments in painting and sculpture. Duchamp has had an immense impact on twentieth-century and twenty first-century art, and he had a seminal influence on the development of conceptual art. By World War I, he had rejected the work of many of his fellow artists as "retinal" art, intended only to please the eye. Instead, Duchamp wanted to use art to serve the mind.

John Cage American avant-garde composer

John Milton Cage Jr. was an American composer, music theorist, artist, and philosopher. A pioneer of indeterminacy in music, electroacoustic music, and non-standard use of musical instruments, Cage was one of the leading figures of the post-war avant-garde. Critics have lauded him as one of the most influential composers of the 20th century. He was also instrumental in the development of modern dance, mostly through his association with choreographer Merce Cunningham, who was also Cage's romantic partner for most of their lives.

While it is easy to dismiss these assertions, further investigation [ who? ] shows that Duchamp and Cage are not so easily disproved. For example, if a pianist plays a Chopin etude, but his finger slips missing one note, is it still the Chopin etude or a new piece of music entirely? Most people would agree that it is still a Chopin etude (albeit with a missing note), which brings into play the Sorites paradox, mentioned below. If one accepts that this is not a fundamentally changed work of music, however, is one implicitly agreeing with Cage that it is merely the duration and context of musical performance, rather than the precise content, which determines what music is? Hence, the question is what the criteria for art objects are and whether these criteria are entirely context-dependent.

Sorites paradox paradox that, if ① one million grains of sand is a heap of sand and ② a heap of sand minus one grain is still a heap, then it follows that one grain of sand is a heap

The sorites paradox is a paradox that arises from vague predicates. A typical formulation involves a heap of sand, from which grains are individually removed. Under the assumption that removing a single grain does not turn a heap into a non-heap, the paradox is to consider what happens when the process is repeated enough times: is a single remaining grain still a heap? If not, when did it change from a heap to a non-heap?

Philosophy of language


A counterfactual statement is a conditional statement with a false antecedent. For example, the statement "If Joseph Swan had not invented the modern incandescent light bulb, then someone else would have invented it anyway" is a counterfactual, because in fact, Joseph Swan invented the modern incandescent light bulb. The most immediate task concerning counterfactuals is that of explaining their truth-conditions. As a start, one might assert that background information is assumed when stating and interpreting counterfactual conditionals and that this background information is just every true statement about the world as it is (pre-counterfactual). In the case of the Swan statement, we have certain trends in the history of technology, the utility of artificial light, the discovery of electricity, and so on. We quickly encounter an error with this initial account: among the true statements will be "Joseph Swan did invent the modern incandescent light bulb." From the conjunction of this statement (call it "S") and the antecedent of the counterfactual ("¬S"), we can derive any conclusion, and we have the unwelcome result that any statement follows from any counterfactual (see the principle of explosion). Nelson Goodman takes up this and related issues in his seminal Fact, Fiction, and Forecast; and David Lewis's influential articulation of possible world theory is popularly applied in efforts to solve it.

Joseph Swan British physicist and inventor

Sir Joseph Wilson Swan FRS was an English physicist, chemist, and inventor. He is known as an independent early developer of a successful incandescent light bulb, and is the person responsible for developing and supplying the first incandescent lights used to illuminate homes and public buildings, including the Savoy Theatre, London, in 1881.

Incandescent light bulb Electric light with a wire filament heated until it glows

An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated to such a high temperature that it glows with visible light (incandescence). The filament is protected from oxidation with a glass or fused quartz bulb that is filled with inert gas or a vacuum. In a halogen lamp, filament evaporation is slowed by a chemical process that redeposits metal vapor onto the filament, thereby extending its life.

The principle of explosion, or the principle of Pseudo-Scotus, is the law of classical logic, intuitionistic logic and similar logical systems, according to which any statement can be proven from a contradiction. That is, once a contradiction has been asserted, any proposition can be inferred from it. This is known as deductive explosion. The proof of this principle was first given by 12th century French philosopher William of Soissons.


Epistemological problems are concerned with the nature, scope and limitations of knowledge. Epistemology may also be described as the study of knowledge.

Epistemology A branch of philosophy concerned with the nature and scope of knowledge

Epistemology is the branch of philosophy concerned with the theory of knowledge.

Gettier problem

Plato suggests, in his Theaetetus (210a) and Meno (97a–98b), that "knowledge" may be defined as justified true belief. For over two millennia, this definition of knowledge has been reinforced and accepted by subsequent philosophers. An item of information's justifiability, truth, and belief have been seen as the necessary and sufficient conditions for knowledge..

In 1963, Edmund Gettier published an article in the journal Analysis , a peer reviewed academic journal of philosophy, entitled "Is Justified True Belief Knowledge?" which offered instances of justified true belief that do not conform to the generally understood meaning of "knowledge." Gettier's examples hinged on instances of epistemic luck: cases where a person appears to have sound evidence for a proposition, and that proposition is in fact true, but the apparent evidence is not causally related to the proposition's truth.

In response to Gettier's article, numerous philosophers[ who? ] have offered modified criteria for "knowledge." There is no general consensus to adopt any of the modified definitions yet proposed. Finally, if infallibilism is true, that would seem to definitively solve the Gettier problem for good--the idea is that knowledge requires certainty, such that, certainty is what serves to bridge the gap so that we arrive at knowledge, which means we would have an adequate definition of knowledge. However, infallibilism is rejected by the overwhelming majority of philosophers/epistemologists, even though it would solve the Gettier problem (if true).

Problem of the criterion

Overlooking for a moment the complications posed by Gettier problems, philosophy has essentially continued to operate on the principle that knowledge is justified true belief. The obvious question that this definition entails is how one can know whether one's justification is sound. One must therefore provide a justification for the justification. That justification itself requires justification, and the questioning continues interminably.

The conclusion is that no one can truly have knowledge of anything, since it is, due to this infinite regression, impossible to satisfy the justification element. In practice, this has caused little concern to philosophers, since the demarcation between a reasonably exhaustive investigation and superfluous investigation is usually clear.

Others argue for forms of coherentist systems, e.g. Susan Haack. Recent work by Peter D. Klein [1] views knowledge as essentially defeasible. Therefore, an infinite regress is unproblematic, since any known fact may be overthrown on sufficiently in-depth investigation.

Molyneux problem

The Molyneux problem dates back to the following question posed by William Molyneux to John Locke in the 17th century: if a man born blind, and able to distinguish by touch between a cube and a globe, were made to see, could he now tell by sight which was the cube and which the globe, before he touched them? The problem raises fundamental issues in epistemology and the philosophy of mind, and was widely discussed after Locke included it in the second edition of his Essay Concerning Human Understanding . [2]

A similar problem was also addressed earlier in the 12th century by Ibn Tufail (Abubacer), in his philosophical novel, Hayy ibn Yaqdhan (Philosophus Autodidactus). His version of the problem, however, dealt mainly with colors rather than shapes. [3] [4]

Modern science may now have the tools necessary to test this problem in controlled environments. The resolution of this problem is in some sense provided by the study of human subjects who gain vision after extended congenital blindness. In one such study, subjects were unable to immediately link objects known by touch to their visual appearance, and only gradually developed the ability to do so over a period of days or months. [5] [6] [7] This indicates that this may no longer be an unsolved problem in philosophy.

Münchhausen trilemma

The Münchhausen trilemma, also called Agrippa's trilemma, purports that it is impossible to prove any certain truth even in fields such as logic and mathematics. According to this argument, the proof of any theory rests either on circular reasoning, infinite regress, or unproven axioms.


The question hinges on whether color is a product of the mind or an inherent property of objects. While most philosophers will agree that color assignment corresponds to spectra of light frequencies, it is not at all clear whether the particular psychological phenomena of color are imposed on these visual signals by the mind, or whether such qualia are somehow naturally associated with their noumena. Another way to look at this question is to assume two people ("Fred" and "George" for the sake of convenience) see colors differently. That is, when Fred sees the sky, his mind interprets this light signal as blue. He calls the sky "blue." However, when George sees the sky, his mind assigns green to that light frequency. If Fred were able to step into George's mind, he would be amazed that George saw green skies. However, George has learned to associate the word "blue" with what his mind sees as green, and so he calls the sky "blue", because for him the color green has the name "blue." The question is whether blue must be blue for all people, or whether the perception of that particular color is assigned by the mind.

This extends to all areas of the physical reality, where the outside world we perceive is merely a representation of what is impressed upon the senses. The objects we see are in truth wave-emitting (or reflecting) objects which the brain shows to the conscious self in various forms and colors. Whether the colors and forms experienced perfectly match between person to person, may never be known. That people can communicate accurately shows that the order and proportionality in which experience is interpreted is generally reliable. Thus one's reality is, at least, compatible to another person's in terms of structure and ratio.


Moral luck

The problem of moral luck is that some people are born into, live within, and experience circumstances that seem to change their moral culpability when all other factors remain the same.

For instance, a case of circumstantial moral luck: a poor person is born into a poor family, and has no other way to feed himself so he steals his food. Another person, born into a very wealthy family, does very little but has ample food and does not need to steal to get it. Should the poor person be more morally blameworthy than the rich person? After all, it is not this person's fault that they were born into such circumstances, but a matter of "luck".

A related case is resultant moral luck. For instance, two persons behave in a morally culpable way, such as driving carelessly, but end up producing unequal amounts of harm: one strikes a pedestrian and kills him, while the other does not. That one driver caused a death and the other did not is no part of the drivers' intentional actions; yet most observers would likely ascribe greater blame to the driver who killed (compare consequentialism and choice).

The fundamental question of moral luck is how our moral responsibility is changed by factors over which we have no control.

Moral knowledge

Are moral facts possible, what do they consist in, and how do we come to know them? Rightness and wrongness seem strange kinds of entities, and different from the usual properties of things in the world, such as wetness, being red, or solidity. Richmond Campbell [8] has outlined these kinds of issues in his encyclopedia article Moral Epistemology.

In particular, he considers three alternative explanations of moral facts as: theological, (supernatural, the commands of God); non-natural (based on intuitions); or simply natural properties (such as leading to pleasure or to happiness). There are cogent arguments against each of these alternative accounts, he claims, and there has not been any fourth alternative proposed. So the existence of moral knowledge and moral facts remains dubious and in need of further investigation. But moral knowledge supposedly already plays an important part in our everyday thinking, in our legal systems and criminal investigations.

Philosophy of mathematics

Mathematical objects

What are numbers, sets, groups, points, etc.? Are they real objects or are they simply relationships that necessarily exist in all structures? Although many disparate views exist regarding what a mathematical object is, the discussion may be roughly partitioned into two opposing schools of thought: platonism, which asserts that mathematical objects are real, and formalism, which asserts that mathematical objects are merely formal constructions. This dispute may be better understood when considering specific examples, such as the "continuum hypothesis". The continuum hypothesis has been proven independent of the ZF axioms of set theory, so within that system, the proposition can neither be proven true nor proven false. A formalist would therefore say that the continuum hypothesis is neither true nor false, unless you further refine the context of the question. A platonist, however, would assert that there either does or does not exist a transfinite set with a cardinality less than the continuum but greater than any countable set.[ citation needed ] So, regardless of whether it has been proven unprovable, the platonist would argue that an answer nonetheless does exist.


Why there is something rather than nothing

The question about why is there anything at all instead of nothing has been raised or commented on by philosophers including Gottfried Wilhelm Leibniz, [9] Martin Heidegger − who called it the fundamental question of metaphysics [10] [11] − and Ludwig Wittgenstein. [12] The question is general, rather than concerning the existence of anything specific such as the universe/s, the Big Bang, mathematical laws, physical laws, time, consciousness or God.

Problem of universals

Principle of individuation

Related to the quarrel of universals, the principle of individuation is what individuates universals.

Sorites paradox

Otherwise known as the "paradox of the heap", the question regards how one defines a "thing." Is a bale of hay still a bale of hay if you remove one straw? If so, is it still a bale of hay if you remove another straw? If you continue this way, you will eventually deplete the entire bale of hay, and the question is: at what point is it no longer a bale of hay? While this may initially seem like a superficial problem, it penetrates to fundamental issues regarding how we define objects. This is similar to Theseus' paradox and the Continuum fallacy.

Theseus paradox

Also known as the Ship of Theseus, this is a classical paradox on the first branch of metaphysics, Ontology (philosophy of existence & identity). The paradox runs thus: There used to be the great ship of Theseus which was made out of, say, 100 parts. Each part has a single corresponding replacement part in the ship's storeroom. The ship then sets out on a voyage. The ship sails through monster-infested waters, and every day, a single piece is damaged and has to be replaced. On the hundredth day, the ship sails back to port, the voyage completed. Through the course of this journey, everything on the ship has been replaced. So, is the ship sailing back home the ship of Theseus or no?

If yes, consider this: the broken original parts are repaired and re-assembled. Is this the ship of Theseus or no? If no, let us name the ship that sails into port "The Argo". At what point (during the journey) did the crew of the Theseus become the crew of the Argo? And what ship is sailing on the fiftieth day? If both the ships trade a single piece, are they still the same ships?

This paradox is a minor variation of the Sorites Paradox above, and has many variations itself. Both sides of the paradox have convincing arguments and counter-arguments, though no one is close to proving it completely.

Material implication

People have a pretty clear idea what if-then means. In formal logic however, material implication defines if-then, which is not consistent with the common understanding of conditionals. In formal logic, the statement "If today is Saturday, then 1+1=2" is true. However, '1+1=2' is true regardless of the content of the antecedent; a causal or meaningful relation is not required. The statement as a whole must be true, because 1+1=2 cannot be false. (If it could, then on a given Saturday, so could the statement). Formal logic has shown itself extremely useful in formalizing argumentation, philosophical reasoning, and mathematics. The discrepancy between material implication and the general conception of conditionals however is a topic of intense investigation: whether it is an inadequacy in formal logic, an ambiguity of ordinary language, or as championed by H. P. Grice, that no discrepancy exists.

Philosophy of mind

Mind–body problem

The mind–body problem is the problem of determining the relationship between the human body and the human mind. Philosophical positions on this question are generally predicated on either a reduction of one to the other, or a belief in the discrete coexistence of both. This problem is usually exemplified by Descartes, who championed a dualistic picture. The problem therein is to establish how the mind and body communicate in a dualistic framework. Neurobiology and emergence have further complicated the problem by allowing the material functions of the mind to be a representation of some further aspect emerging from the mechanistic properties of the brain. The brain essentially stops generating conscious thought during deep sleep; the ability to restore such a pattern remains a mystery to science and is a subject of current research (see also neurophilosophy).

Cognition and AI

This problem actually defines a field, however its pursuits are specific and easily stated. Firstly, what are the criteria for intelligence? What are the necessary components for defining consciousness? Secondly, how can an outside observer test for these criteria? The "Turing Test" is often cited as a prototypical test of intelligence, although it is almost universally regarded as insufficient. It involves a conversation between a sentient being and a machine, and if the being can't tell he is talking to a machine, it is considered intelligent. A well trained machine, however, could theoretically "parrot" its way through the test. This raises the corollary question of whether it is possible to artificially create consciousness (usually in the context of computers or machines), and of how to tell a well-trained mimic from a sentient entity.

Important thought in this area includes most notably: John Searle's Chinese Room, Hubert Dreyfus' non-cognitivist critique, as well as Hilary Putnam's work on Functionalism.

A related field is the ethics of artificial intelligence, which addresses such problems as the existence of moral personhood of AIs, the possibility of moral obligations to AIs (for instance, the right of a possibly sentient computer system to not be turned off), and the question of making AIs that behave ethically towards humans and others.

Hard problem of consciousness

The hard problem of consciousness is the question of what consciousness is and why we have consciousness as opposed to being philosophical zombies. The adjective "hard" is to contrast with the "easy" consciousness problems, which seek to explain the mechanisms of consciousness ("why" versus "how", or final cause versus efficient cause). The hard problem of consciousness is questioning whether all beings undergo an experience of consciousness rather than questioning the neurological makeup of beings.

Philosophy of science

Problem of induction

Intuitively, it seems to be the case that we know certain things with absolute, complete, utter, unshakable certainty. For example, if you travel to the Arctic and touch an iceberg, you know that it would feel cold. These things that we know from experience are known through induction. The problem of induction in short; (1) any inductive statement (like the sun will rise tomorrow) can only be deductively shown if one assumes that nature is uniform. (2) the only way to show that nature is uniform is by using induction. Thus induction cannot be justified deductively.

Demarcation problem

‘The problem of demarcation’ is an expression introduced by Karl Popper to refer to ‘the problem of finding a criterion which would enable us to distinguish between the empirical sciences on the one hand, and mathematics and logic as well as "metaphysical" systems on the other’. Popper attributes this problem to Kant. Although Popper mentions mathematics and logic, other writers focus on distinguishing science from metaphysics.


Does a world independent of human beliefs and representations exist? Is such a world empirically accessible, or would such a world be forever beyond the bounds of human sense and hence unknowable? Can human activity and agency change the objective structure of the world? These questions continue to receive much attention in the philosophy of science. A clear "yes" to the first question is a hallmark of the scientific realism perspective. Philosophers such as Bas van Fraassen have important and interesting answers to the second question. In addition to the realism vs. empiricism axis of debate, there is a realism vs. social constructivism axis which heats many academic passions. With respect to the third question, Paul Boghossian's "Fear of Knowledge: Against Relativism and Constructivism". Oxford University Press. 2006. is a powerful critique of social constructivism, for instance. Ian Hacking's The Social Construction of What? (Harvard UP, 2000) constitutes a more moderate critique of constructivism, which usefully disambiguates confusing polysemy of the term "constructivism."


Philosophical progress

Does philosophical progress occur? Is it even possible?

See also

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Swampman is the subject of a philosophical thought experiment introduced by Donald Davidson in his 1987 paper "Knowing One's Own Mind".

Edmund L. Gettier III is an American philosopher and Professor Emeritus at the University of Massachusetts Amherst. He is best known for his short 1963 article "Is Justified True Belief Knowledge?", which has generated an extensive philosophical literature trying to respond to what became known as the Gettier problem.

The Gettier problem, in the field of epistemology, is a landmark philosophical problem concerning our understanding of descriptive knowledge. Attributed to American philosopher Edmund Gettier, Gettier-type counterexamples challenge the long-held justified true belief (JTB) account of knowledge. The JTB account holds that knowledge is equivalent to justified true belief; if all three conditions are met of a given claim, then we have knowledge of that claim. In his 1963 three-page paper titled "Is Justified True Belief Knowledge?", Gettier attempts to illustrate by means of two counterexamples that there are cases where individuals can have a justified, true belief regarding a claim but still fail to know it because the reasons for the belief, while justified, turn out to be false. Thus, Gettier claims to have shown that the JTB account is inadequate; that it does not account for all of the necessary and sufficient conditions for knowledge.

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In the metaphysics of identity, the ship of Theseus is a thought experiment that raises the question of whether an object that has had all of its components replaced remains fundamentally the same object.

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Is–ought problem

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David Lewis (philosopher) American philosopher

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(i) Possible worlds exist.
(ii) Every possible world is a concrete entity.
(iii) Any possible world is causally and spatiotemporally isolated from any other possible world.
(iv) Our world is among the possible worlds.

Contextualism describes a collection of views in philosophy which emphasize the context in which an action, utterance, or expression occurs, and argues that, in some important respect, the action, utterance, or expression can only be understood relative to that context. Contextualist views hold that philosophically controversial concepts, such as "meaning P", "knowing that P", "having a reason to A", and possibly even "being true" or "being right" only have meaning relative to a specified context. Some philosophers hold that context-dependence may lead to relativism;.

Experimental philosophy is an emerging field of philosophical inquiry that makes use of empirical data—often gathered through surveys which probe the intuitions of ordinary people—in order to inform research on philosophical questions. This use of empirical data is widely seen as opposed to a philosophical methodology that relies mainly on a priori justification, sometimes called "armchair" philosophy, by experimental philosophers. Experimental philosophy initially began by focusing on philosophical questions related to intentional action, the putative conflict between free will and determinism, and causal vs. descriptive theories of linguistic reference. However, experimental philosophy has continued to expand to new areas of research.


  1. Klein, P. D., “Human Knowledge and the Infinite Progress of Reasoning,” Philosophical Studies, 134. 1, 2007, 1-17.
  2. Locke, John. An Essay Concerning Human Understanding , Book 2, Chapter 9.
    I shall here insert a problem of that very ingenious and studious promoter of real knowledge, the learned and worthy Mr. Molyneux, which he was pleased to send me in a letter some months since; and it is this:—"Suppose a man born blind, and now adult, and taught by his touch to distinguish between a cube and a sphere of the same metal, and nighly of the same bigness, so as to tell, when he felt one and the other, which is the cube, which the sphere. Suppose then the cube and sphere placed on a table, and the blind man be made to see: quaere, whether by his sight, before he touched them, he could now distinguish and tell which is the globe, which the cube?" To which the acute and judicious proposer answers, "Not. For, though he has obtained the experience of how a globe, how a cube affects his touch, yet he has not yet obtained the experience, that what affects his touch so or so, must affect his sight so or so; or that a protuberant angle in the cube, that pressed his hand unequally, shall appear to his eye as it does in the cube."—I agree with this thinking gentleman, whom I am proud to call my friend, in his answer to this problem; and am of opinion that the blind man, at first sight, would not be able with certainty to say which was the globe, which the cube, whilst he only saw them; though he could unerringly name them by his touch, and certainly distinguish them by the difference of their figures felt. This I have set down, and leave with my reader, as an occasion for him to consider how much he may be beholden to experience, improvement, and acquired notions, where he thinks he had not the least use of, or help from them. And the rather, because this observing gentleman further adds, that "having, upon the occasion of my book, proposed this to divers very ingenious men, he hardly ever met with one that at first gave the answer to it which he thinks true, till by hearing his reasons they were convinced.
  3. Muhammad ibn Abd al-Malik Ibn Tufayl and Léon Gauthier (1981), Risalat Hayy ibn Yaqzan, p. 5, Editions de la Méditerranée.
    If you want a comparison that will make you clearly grasp the difference between the perception, such as it is understood by that sect [the Sufis] and the perception as others understand it, imagine a person born blind, endowed however with a happy natural temperament, with a lively and firm intelligence, a sure memory, a straight sprite, who grew up from the time he was an infant in a city where he never stopped learning, by means of the senses he did dispose of, to know the inhabitants individually, the numerous species of beings, living as well as non-living, there, the streets and sidestreets, the houses, the steps, in such a manner as to be able to cross the city without a guide, and to recognize immediately those he met; the colors alone would not be known to him except by the names they bore, and by certain definitions that designated them. Suppose that he had arrived at this point and suddenly, his eyes were opened, he recovered his view, and he crosses the entire city, making a tour of it. He would find no object different from the idea he had made of it; he would encounter nothing he didn’t recognize, he would find the colors conformable to the descriptions of them that had been given to him; and in this there would only be two new important things for him, one the consequence of the other: a clarity, a greater brightness, and a great voluptuousness.
  4. Lobel, Diana. A Sufi-Jewish Dialogue: Philosophy and Mysticism in Baḥya Ibn Paqūda's Duties of the Heart, University of Pennsylvania Press, 2006, p.24. ISBN   0-8122-3953-9
  5. Held, R.; Ostrovsky, Y.; De Gelder, B.; Gandhi, T.; Ganesh, S.; Mathur, U.; Sinha, P. (2011). "The newly sighted fail to match seen with felt". Nature Neuroscience. 14 (5): 551–553. doi:10.1038/nn.2795. PMID   21478887.
  6. "Scientists settle centuries-old debate on perception".
  7. Crawford, Hayley. "Mapping touch to sight takes time to learn". New Scientist.
  8. Campbell, Richmond (February 4, 2003). "Moral Epistemology" via
  9. "why is there something rather than nothing?", section 7, "Principles of Nature and Grace"
  10. "The Fundamental Question". Retrieved 26 April 2017.
  11. Geier, Manfred. Wittgenstein und Heidegger: Die letzten Philosophen (in German). Rowohlt Verlag. ISBN   9783644045118 . Retrieved 26 April 2017.
  12. "Not how the world is, is the mystical, but that it is." Tractatus Logico-Philosophicus 6.44