Early empiricism Between 600 and 200 BCE, the
Vaisheshika school of Hindu philosophy, founded by the ancient Indian philosopher
Kanada, accepted
perception and
inference as the only two reliable sources of knowledge. This is enumerated in his work
Vaiśeṣika Sūtra. The
Charvaka school held similar beliefs, asserting that perception is the only reliable source of knowledge while inference obtains knowledge with uncertainty. The earliest Western proto-empiricists were the
empiric school of ancient Greek medical practitioners, founded in 330 BCE. Its members rejected the doctrines of the
dogmatic school, preferring to rely on the observation of
phantasiai (i.e., phenomena, the appearances). The Empiric school was closely allied with the
Pyrrhonist school of philosophy, which made the philosophical case for their proto-empiricism. The notion of
tabula rasa ("clean slate" or "blank tablet") connotes a view of the mind as an originally blank or empty recorder (Locke used the words "white paper") on which experience leaves marks. This denies that humans have
innate ideas. The notion dates back to
Aristotle, : Aristotle's explanation of how this was possible was not strictly empiricist in a modern sense, but rather based on his theory of
potentiality and actuality, and experience of sense perceptions still requires the help of the
active nous. These notions contrasted with
Platonic notions of the human mind as an entity that pre-existed somewhere in the heavens, before being sent down to join a body on Earth (see Plato's
Phaedo and
Apology, as well as others). Aristotle was considered to give a more important position to sense perception than
Plato, and commentators in the Middle Ages summarized one of his positions as "
nihil in intellectu nisi prius fuerit in sensu" (Latin for "nothing in the intellect without first being in the senses"). This idea was later developed in ancient philosophy by the
Stoic school, from about 330 BCE. Stoic epistemology generally emphasizes that the mind starts blank, but acquires knowledge as the outside world is impressed upon it. The doxographer
Aetius summarizes this view as "When a man is born, the Stoics say, he has the commanding part of his soul like a sheet of paper ready for writing upon." (Avicenna) from 1271
Islamic Golden Age and Pre-Renaissance (5th to 15th centuries CE) During the
Middle Ages (from the 5th to the 15th century CE) Aristotle's theory of
tabula rasa was developed by
Islamic philosophers starting with
Al Farabi (), developing into an elaborate theory by
Avicenna (c. 980 – 1037 CE) So the immaterial "active intellect", separate from any individual person, is still essential for understanding to occur. In the 12th century CE, the
Andalusian Muslim philosopher and novelist Abu Bakr
Ibn Tufail (known as "Abubacer" or "Ebu Tophail" in the West) included the theory of
tabula rasa as a
thought experiment in his
Arabic philosophical novel,
Hayy ibn Yaqdhan in which he depicted the development of the mind of a
feral child "from a
tabula rasa to that of an adult, in complete isolation from society" on a
desert island, through experience alone. The
Latin translation of his
philosophical novel, entitled
Philosophus Autodidactus, published by
Edward Pococke the Younger in 1671, had an influence on
John Locke's formulation of
tabula rasa in
An Essay Concerning Human Understanding. A similar
Islamic theological novel,
Theologus Autodidactus, was written by the Arab theologian and physician
Ibn al-Nafis in the 13th century. It also dealt with the theme of empiricism through the story of a feral child on a desert island, but departed from its predecessor by depicting the development of the protagonist's mind through contact with society rather than in isolation from society. During the 13th century
Thomas Aquinas adopted into
scholasticism the
Aristotelian position that the senses are essential to the mind.
Bonaventure (1221–1274), one of Aquinas' strongest intellectual opponents, offered some of the strongest arguments in favour of the Platonic idea of the mind.
Renaissance Italy In the late
renaissance various writers began to question the
medieval and
classical understanding of knowledge acquisition in a more fundamental way. In political and historical writing
Niccolò Machiavelli and his friend
Francesco Guicciardini initiated a new realistic style of writing. Machiavelli in particular was scornful of writers on politics who judged everything in comparison to mental ideals and demanded that people should study the "effectual truth" instead. Their contemporary,
Leonardo da Vinci (1452–1519) said, "If you find from your own experience that something is a fact and it contradicts what some authority has written down, then you must abandon the authority and base your reasoning on your own findings." Significantly, an empirical metaphysical system was developed by the Italian philosopher
Bernardino Telesio which had an enormous impact on the development of later Italian thinkers, including Telesio's students
Antonio Persio and
Sertorio Quattromani, his contemporaries
Thomas Campanella and
Giordano Bruno, and later British philosophers such as
Francis Bacon, who regarded Telesio as "the first of the moderns". Telesio's influence can also be seen on the French philosophers
René Descartes and
Pierre Gassendi. In response to the early-to-mid-17th-century "
continental rationalism",
John Locke (1632–1704) proposed in
An Essay Concerning Human Understanding (1689) a very influential view wherein the
only knowledge humans can have is
a posteriori, i.e., based upon experience. Locke is famously attributed with holding the proposition that the human mind is a
tabula rasa, a "blank tablet", in Locke's words "white paper", on which the experiences derived from sense impressions as a person's life proceeds are written. There are two sources of our ideas: sensation and reflection. In both cases, a distinction is made between simple and complex ideas. The former are unanalysable, and are broken down into primary and secondary qualities. Primary qualities are essential for the object in question to be what it is. Without specific primary qualities, an object would not be what it is. For example, an apple is an apple because of the arrangement of its atomic structure. If an apple were structured differently, it would cease to be an apple. Secondary qualities are the sensory information we can perceive from its primary qualities. For example, an apple can be perceived in various colours, sizes, and textures but it is still identified as an apple. Therefore, its primary qualities dictate what the object essentially is, while its secondary qualities define its attributes. Complex ideas combine simple ones, and divide into substances, modes, and relations. According to Locke, our knowledge of things is a perception of ideas that are in accordance or discordance with each other, which is very different from the quest for
certainty of
Descartes. A generation later, the Irish
Anglican bishop
George Berkeley (1685–1753) determined that Locke's view immediately opened a door that would lead to eventual
atheism. In response to Locke, he put forth in his
Treatise Concerning the Principles of Human Knowledge (1710) an important challenge to empiricism in which things
only exist either as a
result of their being perceived, or by virtue of the fact that they are an entity doing the perceiving. (For Berkeley, God fills in for humans by doing the perceiving whenever humans are not around to do it.) In his text
Alciphron, Berkeley maintained that any order humans may see in nature is the language or handwriting of God. Berkeley's approach to empiricism would later come to be called
subjective idealism. And, Hume divided all of human knowledge into two categories:
relations of ideas and
matters of fact (see also
Kant's analytic-synthetic distinction). Mathematical and logical propositions (e.g. "that the square of the hypotenuse is equal to the sum of the squares of the two sides") are examples of the first, while propositions involving some
contingent observation of the world (e.g. "the sun rises in the East") are examples of the second. All of people's "ideas", in turn, are derived from their "impressions". For Hume, an "impression" corresponds roughly with what we call a sensation. To remember or to imagine such impressions is to have an "idea". Ideas are therefore the faint copies of sensations. Hume concluded that such things as belief in an external world and belief in the existence of the self were not rationally justifiable. According to Hume these beliefs were to be accepted nonetheless because of their profound basis in instinct and custom. Hume's lasting legacy, however, was the doubt that his skeptical arguments cast on the legitimacy of inductive reasoning, allowing many skeptics who followed to cast similar doubt.
Phenomenalism Most of Hume's followers have disagreed with his conclusion that belief in an external world is
rationally unjustifiable, contending that Hume's own principles implicitly contained the rational justification for such a belief, that is, beyond being content to let the issue rest on human instinct, custom and habit. According to an extreme empiricist theory known as
phenomenalism, anticipated by the arguments of both Hume and George Berkeley, a physical object is a kind of construction out of our experiences. Phenomenalism is the view that physical objects, properties, events (whatever is physical) are reducible to mental objects, properties, events. Ultimately, only mental objects, properties, events, exist—hence the closely related term
subjective idealism. By the phenomenalistic line of thinking, to have a visual experience of a real physical thing is to have an experience of a certain kind of group of experiences. This type of set of experiences possesses a constancy and coherence that is lacking in the set of experiences of which hallucinations, for example, are a part. As
John Stuart Mill put it in the mid-19th century, matter is the "permanent possibility of sensation". Mill's empiricism went a significant step beyond Hume in still another respect: in maintaining that induction is necessary for
all meaningful knowledge including mathematics. As summarized by D.W. Hamlin: Mill's empiricism thus held that knowledge of any kind is not from direct experience but an inductive inference from direct experience. The problems other philosophers have had with Mill's position center around the following issues: Firstly, Mill's formulation encounters difficulty when it describes what direct experience is by differentiating only between actual and possible sensations. This misses some key discussion concerning conditions under which such "groups of permanent possibilities of sensation" might exist in the first place. Berkeley put God in that gap; the phenomenalists, including Mill, essentially left the question unanswered. In the end, lacking an acknowledgement of an aspect of "reality" that goes beyond mere "possibilities of sensation", such a position leads to a version of subjective idealism. Questions of how floor beams continue to support a floor while unobserved, how trees continue to grow while unobserved and untouched by human hands, etc., remain unanswered, and perhaps unanswerable in these terms. Secondly, Mill's formulation leaves open the unsettling possibility that the "gap-filling entities are purely possibilities and not actualities at all". The phenomenalist phase of post-Humean empiricism ended by the 1940s, for by that time it had become obvious that statements about physical things could not be translated into statements about actual and possible sense data. If a physical object statement is to be translatable into a sense-data statement, the former must be at least deducible from the latter. But it came to be realized that there is no finite set of statements about actual and possible sense-data from which we can deduce even a single physical-object statement. The translating or paraphrasing statement must be couched in terms of normal observers in normal conditions of observation. There is, however, no
finite set of statements that are couched in purely sensory terms and can express the satisfaction of the condition of the presence of a normal observer. According to phenomenalism, to say that a normal observer is present is to make the hypothetical statement that were a doctor to inspect the observer, the observer would appear to the doctor to be normal. But, of course, the doctor himself must be a normal observer. If we are to specify this doctor's normality in sensory terms, we must make reference to a second doctor who, when inspecting the sense organs of the first doctor, would himself have to have the sense data a normal observer has when inspecting the sense organs of a subject who is a normal observer. And if we are to specify in sensory terms that the second doctor is a normal observer, we must refer to a third doctor, and so on (also see the
third man).
Logical empiricism Logical empiricism (also
logical positivism or
neopositivism) was an early 20th-century attempt to synthesize the essential ideas of British empiricism (e.g. a strong emphasis on sensory experience as the basis for knowledge) with certain insights from
mathematical logic that had been developed by
Gottlob Frege and
Ludwig Wittgenstein. Some of the key figures in this movement were
Otto Neurath,
Moritz Schlick and the rest of the
Vienna Circle, along with
A. J. Ayer,
Rudolf Carnap and
Hans Reichenbach. The neopositivists subscribed to a notion of philosophy as the conceptual clarification of the methods, insights and discoveries of the sciences. They saw in the logical symbolism elaborated by Frege (1848–1925) and
Bertrand Russell (1872–1970) a powerful instrument that could rationally reconstruct all scientific discourse into an ideal, logically perfect, language that would be free of the ambiguities and deformations of natural language. This gave rise to what they saw as metaphysical pseudoproblems and other conceptual confusions. By combining Frege's thesis that all mathematical truths are logical with the early Wittgenstein's idea that all
logical truths are mere linguistic
tautologies, they arrived at a twofold classification of all propositions: the "analytic" (
a priori) and the "synthetic" (
a posteriori). On this basis, they formulated a strong principle of demarcation between sentences that have sense and those that do not: the so-called "
verification principle". Any sentence that is not purely logical, or is unverifiable, is devoid of meaning. As a result, most metaphysical, ethical, aesthetic and other traditional philosophical problems came to be considered pseudoproblems. In the extreme empiricism of the neopositivists—at least before the 1930s—any genuinely synthetic assertion must be reducible to an ultimate assertion (or set of ultimate assertions) that expresses direct observations or perceptions. In later years, Carnap and Neurath abandoned this sort of
phenomenalism in favor of a rational reconstruction of knowledge into the language of an objective spatio-temporal physics. That is, instead of translating sentences about physical objects into sense-data, such sentences were to be translated into so-called
protocol sentences, for example, "
X at location
Y and at time
T observes such and such". The central theses of logical positivism (verificationism, the analytic–synthetic distinction, reductionism, etc.) came under sharp attack after World War II by thinkers such as
Nelson Goodman,
W. V. Quine,
Hilary Putnam,
Karl Popper, and
Richard Rorty. By the late 1960s, it had become evident to most philosophers that the movement had pretty much run its course, though its influence is still significant among contemporary
analytic philosophers such as
Michael Dummett and other
anti-realists.
Pragmatism In the late 19th and early 20th century, several forms of
pragmatic philosophy arose. The ideas of pragmatism, in its various forms, developed mainly from discussions between
Charles Sanders Peirce and
William James when both men were at Harvard in the 1870s. James popularized the term "pragmatism", giving Peirce full credit for its patrimony, but Peirce later demurred from the tangents that the movement was taking, and redubbed what he regarded as the original idea with the name of "pragmaticism". Along with its
pragmatic theory of truth, this perspective integrates the basic insights of empirical (experience-based) and
rational (concept-based) thinking. Charles Peirce (1839–1914) was highly influential in laying the groundwork for today's empirical
scientific method. Although Peirce severely criticized many elements of Descartes' peculiar brand of rationalism, he did not reject rationalism outright. Indeed, he concurred with the main ideas of rationalism, most importantly the idea that rational concepts can be meaningful and the idea that rational concepts necessarily go beyond the data given by empirical observation. In later years he even emphasized the concept-driven side of the then ongoing debate between strict empiricism and strict rationalism, in part to counterbalance the excesses to which some of his cohorts had taken pragmatism under the "data-driven" strict-empiricist view. Among Peirce's major contributions was to place
inductive reasoning and
deductive reasoning in a complementary rather than competitive mode, the latter of which had been the primary trend among the educated since David Hume wrote a century before. To this, Peirce added the concept of
abductive reasoning. The combined three forms of reasoning serve as a primary conceptual foundation for the empirically based scientific method today. Peirce's approach "presupposes that (1) the objects of knowledge are real things, (2) the characters (properties) of real things do not depend on our perceptions of them, and (3) everyone who has sufficient experience of real things will agree on the truth about them. According to Peirce's doctrine of
fallibilism, the conclusions of science are always tentative. The rationality of the scientific method does not depend on the certainty of its conclusions, but on its self-corrective character: by continued application of the method science can detect and correct its own mistakes, and thus eventually lead to the discovery of truth". In his Harvard "Lectures on Pragmatism" (1903), Peirce enumerated what he called the "three cotary propositions of pragmatism" (
L: cos, cotis whetstone), saying that they "put the edge on the
maxim of pragmatism". First among these, he listed the peripatetic-thomist observation mentioned above, but he further observed that this link between sensory perception and intellectual conception is a two-way street. That is, it can be taken to say that whatever we find in the intellect is also incipiently in the senses. Hence, if theories are theory-laden then so are the senses, and perception itself can be seen as a species of
abductive inference, its difference being that it is beyond control and hence beyond critique—in a word, incorrigible. This in no way conflicts with the fallibility and revisability of scientific concepts, since it is only the immediate percept in its unique individuality or "thisness"—what the
Scholastics called its
haecceity—that stands beyond control and correction. Scientific concepts, on the other hand, are general in nature, and transient sensations do in another sense find correction within them. This notion of perception as abduction has received periodic revivals in
artificial intelligence and
cognitive science research, most recently for instance with the work of
Irvin Rock on
indirect perception. Around the beginning of the 20th century, William James (1842–1910) coined the term "
radical empiricism" to describe an offshoot of his form of pragmatism, which he argued could be dealt with separately from his pragmatism—though in fact the two concepts are intertwined in James's published lectures. James maintained that the empirically observed "directly apprehended universe needs ... no extraneous trans-empirical connective support", by which he meant to rule out the perception that there can be any
value added by seeking
supernatural explanations for
natural phenomena. James' "radical empiricism" is thus
not radical in the context of the term "empiricism", but is instead fairly consistent with the modern use of the term "
empirical". His method of argument in arriving at this view, however, still readily encounters debate within philosophy even today.
John Dewey (1859–1952) modified James' pragmatism to form a theory known as
instrumentalism. The role of sense experience in Dewey's theory is crucial, in that he saw experience as a unified totality of things through which everything else is interrelated. Dewey's basic thought, in accordance with empiricism, was that
reality is determined by past experience. Therefore, humans adapt their past experiences of things to perform experiments upon and test the pragmatic values of such experience. The value of such experience is measured experientially and scientifically, and the results of such tests generate ideas that serve as instruments for future experimentation, in physical sciences as in ethics. Thus, ideas in Dewey's system retain their empiricist flavour in that they are only known
a posteriori. ==See also==