If a tree falls in a forest
"If a tree falls in a forest and no one is around to hear it, does it make a sound?" is a philosophical thought experiment
A thought experiment or Gedankenexperiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences...
that raises questions regarding observation
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments. The term may also refer to any data collected during this activity...
and knowledge of reality
In philosophy, reality is the state of things as they actually exist, rather than as they may appear or might be imagined. In a wider definition, reality includes everything that is and has been, whether or not it is observable or comprehensible...
HistoryPhilosopher George Berkeley
George Berkeley , also known as Bishop Berkeley , was an Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism"...
, in his work, A Treatise Concerning the Principles of Human Knowledge, proposes, "But, say you, surely there is nothing easier than for me to imagine trees, for instance, in a park [...] and nobody by to perceive them. [...] The objects of sense exist only when they are perceived; the trees therefore are in the garden [...] no longer than while there is somebody by to perceive them." Nevertheless, Berkeley never actually wrote about the question.
Berkeley's example is referred to by William Fossett twenty years later in a consideration of the emergence of meaning: "[T]ease apart the threads [of the natural world] and the pattern vanishes. The design is in how the cloth-maker arranges the threads: this way and that, as fashion dictates. [...] To say something is meaningful is to say that that is how we arrange it so; how we comprehend it to be, and what is comprehended by you or I may not be by a cat, for example. If a tree falls in a park and there is no-one to hand, it is silent and invisible and nameless. And if we were to vanish, there would be no tree at all; any meaning would vanish along with us. Other than what the cats make of it all, of course."
Some years later, a similar question is posed. It is unknown whether the source of this question is Berkeley or not. In June 1883 in the magazine The Chautauquan, the question was put, "If a tree were to fall on an island where there were no human beings would there be any sound?" They then went on to answer the query with, "No. Sound is the sensation excited in the ear when the air or other medium is set in motion." This seems to imply that the question is posed not from a philosophical viewpoint, but from a purely scientific one. The magazine Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...
corroborated the technical aspect of this question, while leaving out the philosophic side, a year later when they asked the question slightly reworded, "If a tree were to fall on an uninhabited island, would there be any sound?" And gave a more technical answer, "Sound is vibration, transmitted to our senses through the mechanism of the ear, and recognized as sound only at our nerve centers. The falling of the tree or any other disturbance will produce vibration of the air. If there be no ears to hear, there will be no sound."
The current phrasing appears to have originated in the 1910 book Physics by Charles Riborg Mann and George Ransom Twiss. The question "When a tree falls in a lonely forest, and no animal is near by to hear it, does it make a sound? Why?" is posed along with many other questions to quiz readers on the contents of the chapter, and as such, is posed from a purely physical point of view.
The possibility of unperceived existenceCan something exist without being perceived? - Quoted from Pamela Jackson - e.g."is sound only sound if a person hears it?" The most immediate philosophical topic that the riddle introduces involves the existence of the tree (and the sound it produces) outside of human perception. If no one is around to see, hear, touch or smell the tree, how could it be said to exist? What is it to say that it exists when such an existence is unknown? Of course, from a scientific viewpoint, it exists. It is human beings that are able to perceive it. George Berkeley in the 18th century developed subjective idealism
Subjective idealism, or empirical idealism, is the monistic metaphysical doctrine that only minds and mental contents exist. It entails and is generally identified or associated with immaterialism, the doctrine that physical things do not exist...
, a metaphysical
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...
theory to respond to these questions, coined famously as "to be is to be perceived". Today meta-physicians are split. According to substance theory
Substance theory, or substance attribute theory, is an ontological theory about objecthood, positing that a substance is distinct from its properties. A thing-in-itself is a property-bearer that must be distinguished from the properties it bears....
, a substance is distinct from its properties, while according to bundle theory
Bundle theory, originated by the 18th century Scottish philosopher David Hume, is the ontological theory about objecthood in which an object consists only of a collection of properties, relations or tropes....
, an object is merely its sense data
In the philosophy of perception, the theory of sense data was a popular view held the early 20th century by philosophers such as Bertrand Russell, C. D. Broad, H. H. Price, A.J. Ayer and G.E. Moore, among others. Sense data are supposedly mind-dependent objects whose existence and properties are...
. The tree will not make a sound.
Knowledge of the unobserved worldCan we assume the unobserved world functions the same as the observed world? - e.g., "does observation affect outcome?"
A similar question does not involve whether or not an unobserved event occurs predictably, like it occurs when it is observed. The anthropic principle
In astrophysics and cosmology, the anthropic principle is the philosophical argument that observations of the physical Universe must be compatible with the conscious life that observes it. Some proponents of the argument reason that it explains why the Universe has the age and the fundamental...
suggests that the observer, just in its existence, may impose on the reality observed.
However, most people, as well as scientists, assume that the observer doesn't change whether the tree-fall causes a sound or not, but this is an impossible claim to prove. However, many scientists would argue as follows, "A truly unobserved event is one which realises no effect (imparts no information) on any other (where 'other' might be e.g., human, sound-recorder or rock), it therefore can have no legacy in the present (or ongoing) wider physical universe. It may then be recognized that the unobserved event was absolutely identical to an event which did not occur at all.". Of course, the fact that the tree is known to have changed state from 'upright' to 'fallen' implies that the event must be observed to ask the question at all - even if only by the supposed deaf onlooker.
The British philosopher of science Roy Bhaskar
Roy Bhaskar is a British philosopher, best known as the initiator of the philosophical movement of Critical Realism.-Early life:Bhaskar was born in Teddington, London, the elder of two brothers...
, credited with developing critical realism
In the philosophy of perception, critical realism is the theory that some of our sense-data can and do accurately represent external objects, properties, and events, while other of our sense-data do not accurately represent any external objects, properties, and events...
has argued, in apparent reference to this riddle, that:
If men ceased to exist sound would continue to travel and heavy bodies to fall to the earth in exactly the same way, though ex hypothesi there would be no-one to know it
This existence of an unobserved real is integral to Bhaskar's ontology, which contends (in opposition to the various strains of positivism which have dominated both natural and social science in the twentieth century) that 'real structures exist independently of and are often out of phase with the actual patterns of events'. In social science, this has made his approach popular amongst contemporary Marxists - notably Alex Callinicos
Alexander Theodore Callinicos is a Trotskyist political theorist, a member of the Central Committee of the Socialist Workers Party and its International Secretary, and is Director of the Centre for European Studies at King's College London...
- who postulate the existence of real social forces and structures which might not always be observable
The dissimilarity between sensation and realityWhat is the difference between what something is, and how it appears? - e.g., "sound is the variation of pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
that propagates through matter as a wave"
Perhaps the most important topic the riddle offers is the division between perception of an object and how an object really is. If a tree exists outside of perception then there is no way for us to know that the tree exists. So then, what do we mean by 'existence'? Even Disney World, if I say that it exists, independent of the fact that I have never seen, heard, felt, smelled or echo located it, never experienced it, that I 'know' it exists because I have heard tales of it, does not the Disney World exist then in my knowledge, in my perception, in my mind, just like a memory would exist in my mind? So then, what is the difference between perception and reality? Also, people may also say, if the tree exists outside of perception (as common sense
Common sense is defined by Merriam-Webster as, "sound and prudent judgment based on a simple perception of the situation or facts." Thus, "common sense" equates to the knowledge and experience which most people already have, or which the person using the term believes that they do or should have...
would dictate), then it will produce sound waves. However, these sound waves will not actually sound like anything. Sound as it is mechanically understood will occur, but sound as it is understood by sensation will not occur. So then, how is it known that 'sound as it is mechanically understood' will occur if that sound is not perceived?
This riddle illustrates John Locke's
John Locke FRS , widely known as the Father of Liberalism, was an English philosopher and physician regarded as one of the most influential of Enlightenment thinkers. Considered one of the first of the British empiricists, following the tradition of Francis Bacon, he is equally important to social...
famous distinction between primary and secondary qualities
Primary/secondary quality distinction
The primary/secondary quality distinction is a conceptual distinction in epistemology and metaphysics, concerning the nature of reality. It is most explicitly articulated by John Locke in his Essay concerning Human Understanding, but earlier thinkers such as Galileo and Descartes made similar...
. This distinction outlines which qualities are axiomatically imbibed in an object, and which qualities are ascribed to the object. That is, a red thing is not really red (that is, "red" is a secondary quality), a sweet thing is not really sweet, a sound does not actually sound like anything, but a round object is round.
Tibetanfrom The Thirty-Seven Bodhisattva Practices by Ngulchu Thogme Zangpo,
"22 Appearances are one's own mind. From the beginning, mind's nature is free from the extremes of elaboration. Knowing this, not to engage the mind in subject-object duality is the bodhisattva's practice."
There is a well-known story of Hui-neng
Dajian Huineng was a Chinese Chán monastic who is one of the most important figures in the entire tradition, according to standard Zen hagiographies...
, a well-respected Buddhist monk who later became known as the founder of the Zen
Zen is a school of Mahāyāna Buddhism founded by the Buddhist monk Bodhidharma. The word Zen is from the Japanese pronunciation of the Chinese word Chán , which in turn is derived from the Sanskrit word dhyāna, which can be approximately translated as "meditation" or "meditative state."Zen...
school, who one day happened to be passing by some two monks.
- "Two monks were arguing about the temple flag waving in the wind. One said, "The flag moves." The other said, "The wind moves." They argued back and forth but could not agree.
- The Sixth Ancestor said, "Gentlemen! It is not the wind that moves; it is not the flag that moves; it is your mind that moves." The two monks were struck with awe."
- - The Mumonkan Case 29, translation by Robert Aitken
Hui-neng Receives The Dharma
One day the monks at Huang-mei monastery were instructed to write a stanza in order that their master Hung-jen might decide who would inherit the dharma throne. All of the monks assumed that a certain senior disciple Shen-hsui would win and thus didn't even bother writing stanzas. Shen-hsui assumed he would win too, and wrote the following stanza on the monastery wall:
- The body is a BodhiBodhiBodhi is both a Pāli and Sanskrit word traditionally translated into English with the word "enlightenment", but which means awakened. In Buddhism it is the knowledge possessed by a Buddha into the nature of things...
- the mind a standing mirror bright.
- At all times polish it diligently,
- and let no dust alight.
Due to the danger surrounding him if he were to openly challenge the senior monk Shen-hsui, Hui-neng went out one night while it was completely dark and wrote the following stanza in secret:
- Bodhi originally has no tree.
- The bright mirror also has no stand.
- Fundamentally there is not a single thing.
- Where could dust arise?
Later, master Hung-jen saw this stanza and confirmed that he who had written it had indeed opened his mind's eye. Finding it was Hui-neng, master Hung-jen then gave Hui-neng the secret dharma teachings of their lineage, which Hui-neng says completely opened his mind , and gave the young Hui-neng the dharma robe and stick, symbolizing his status as Patriarch of the lineage. Hung-jen told Hui-neng that he must then flee the monastery for fear of Shen-hsui and his followers killing Hui-neng. Hui-neng did as he was told and then later returned from living with some hunters to become The Sixth Patriarch and pass on The Dharma
Dharma means Law or Natural Law and is a concept of central importance in Indian philosophy and religion. In the context of Hinduism, it refers to one's personal obligations, calling and duties, and a Hindu's dharma is affected by the person's age, caste, class, occupation, and gender...
in such forms as The Sutra Spoken by The Sixth Patriarch
The Platform Sutra of the Sixth Patriarch , is a Buddhist scripture that was composed in China. It is one of the seminal texts in the Chan/Zen schools. It is centered on discourses given at Shao Zhou temple attributed to the sixth Chan patriarch, Huineng...
. Hui-neng also started the Sudden School which taught that Mind is realized instantaneously while Shen-hsui started the Gradual School which taught, similar to his stanza above, a sort of dust-wiping meditation. Zen today embodies Hui-neng's Sudden School style, particularly with Satori
is a Japanese Buddhist term for enlightenment that literally means "understanding". In the Zen Buddhist tradition, satori refers to a flash of sudden awareness, or individual enlightenment, and is considered a "first step" or embarkation toward nirvana....
See also There is no spoon from the film The Matrix.
- Object (philosophy)Object (philosophy)An object in philosophy is a technical term often used in contrast to the term subject. Consciousness is a state of cognition that includes the subject, which can never be doubted as only it can be the one who doubts, and some object or objects that may or may not have real existence without...
- Observer effect (physics)Observer effect (physics)In physics, the term observer effect refers to changes that the act of observation will make on the phenomenon being observed. This is often the result of instruments that, by necessity, alter the state of what they measure in some manner...
- Schrödinger's catSchrödinger's catSchrödinger's cat is a thought experiment, usually described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The scenario presents a cat that might be...
- Principle of localityPrinciple of localityIn physics, the principle of locality states that an object is influenced directly only by its immediate surroundings. Experiments have shown that quantum mechanically entangled particles must violate either the principle of locality or the form of philosophical realism known as counterfactual...