Philosophy.

Philosophy is a field of study in which people question, and create theories about, the nature of reality. It includes diverse subfields, such as aesthetics, epistemology, ontology, ethics, logic, metaphysics, and law. Philosophers concern themselves with such fundamental and mysterious topics as the existence or absence of a divine being, the nature of being and the universe, the pursuit of truth, the nature of consciousness, and the morality of actions.There are a number of broad approaches to the subject as a whole which vary according to the traditions of people all over the world. One notable approach is that of Western philosophy, a school of thought which developed in the West and which fundamentally uses reason to evaluate arguments. Eastern philosophy is considered its counterpart. The methodology of philosophy is itself debated within the field of metaphilosophy.

Origin

The term philosophy comes from the Greek word Φιλοσοφία (philo-sophia), which means "love of wisdom." If one were to ask the ancient Greeks for the meaning of "wisdom", their answers would have dwelt on virtue, the quest for genuine knowledge, and the eradication of false opinions. However, the term is notoriously difficult to define today (see definition of philosophy) because of the diverse fields of study to which it has been popularly applied. The Penguin Dictionary of Philosophy defines it as the study of "the most fundamental and general concepts and principles involved in thought, action, and reality". It goes on to observe that philosophy differs from science in that philosophy's questions cannot be answered empirically, and from religion in that philosophy allows no place for faith or revelation. However, these points are called into question by the Oxford Dictionary of Philosophy, which states: "the late 20th-century spirit of the subject [...] prefers to see philosophical reflection as continuous with the best practice of any field of intellectual enquiry". Indeed, many of the speculations of early philosophers in the field of natural philosophy eventually formed the basis for several kinds of modern scientific explanation.

Branches of philosophy

There is no universal agreement about which subjects are the main branches of philosophy. In The Story of Philosophy, Will Durant lists logic, aesthetics, ethics, politics, and metaphysics.
Nevertheless, there are many places where these subjects overlap, and there are many philosophical ideas that cannot be placed neatly into only one of these categories.Each branch has its own particular questions. Logic asks: How do we distinguish arguments from premises to conclusions as valid or invalid? How can we know that a statement is true or false? What kinds of questions can we answer? Aesthetics asks: What is beauty? What is art? Ethics asks: Is there a difference between morally right and wrong actions, values, or institutions? Which actions are right and which are wrong? Are values absolute or relative? What is justice? What are natural laws? What is happiness? Is there a normative value on which all other values depend? Are values 'in' the world (like tables and chairs) and if not, how should we understand their ontological status? Politics is the study of social organization. Professor Durant describes "monarchy, aristocracy, democracy, socialism, anarchism & feminism" as the "dramatis personae of political philosophy". And metaphysics asks: What is reality? What exists? Do things exist independently of perception?Outside these five broad categories are other areas of philosophical inquiry such as religion or theology.

History of philosophy

The history of Western philosophy is traditionally divided into three eras: Ancient philosophy, Medieval philosophy, and Modern philosophy. Eastern philosophy has been, for most of its history, independent of Western philosophy. Some philosophers have argued that human civilization has passed into a new, "post-modern" period. Others believe that there is a distinction between "Modern" philosophy and Contemporary philosophy, but there is great disagreement about the content of this difference.

Western philosophy

Greco-Roman philosophy

Ancient Greek philosophy may be divided into the pre-Socratic period, the Socratic period, and the post-Aristotelian period. The pre-Socratic period was characterized by metaphysical speculation, often preserved in the form of grand, sweeping statements, such as "All is fire", or "All changes". Important pre-Socratic philosophers include Thales, Anaximander, Anaximenes, Democritus, Parmenides, and Heraclitus. The Socratic period is named in honor of the most recognizable figure in Western philosophy, Socrates, who, along with his pupil Plato, revolutionized philosophy through the use of the Socratic method, which developed the very general philosophical methods of definition, analysis, and synthesis. While Socrates wrote nothing himself, his influence as a "skeptic" survives through Plato's works. Plato's writings are often considered basic texts in philosophy as they defined the fundamental issues of philosophy for future generations. These issues and others were taken up by Aristotle, who studied at Plato's school, the Academy, and who often disagreed with what Plato had written. The post-Aristotelian period ushered in such philosophers as Euclid, Epicurus, Chrysippus, Hipparchia the Cynic, Pyrrho, and Sextus Empiricus.

Medieval philosophy

The medieval period of philosophy came with the collapse of Roman civilization and the dawn of Christianity, Islam, and rabbinic Judaism. The medieval period brought Christian scholastic philosophy, with writers such as Augustine of Hippo, Boethius, Anselm, Robert Grosseteste, Albertus Magnus, Roger Bacon, Bonaventure, Thomas Aquinas, John Duns Scotus, William of Ockham, Nicholas of Cusa, and Francisco Suárez. A female Christian philosopher of the period was a student of Abelard named Heloïse. The philosophers in the scholastic Christian tradition and philosophers in the other major Abrahamic religions (such as the Jewish philosophers Saadia Gaon and Maimonides, and the Muslim philosophers Avicenna, Al-Ghazali, and Averroes) were each aware of the others' works. These religious traditions took on questions about the relation of man to God. The philosophy of this period is characterized by analysis of the nature and properties of God; the metaphysics involving substance, essences and accidents (that is, qualities that are respectively essential to substances possessing them or merely happening to be possessed by them), form, and divisibility; and logic and the philosophy of language.Many of these philosophers took as their starting point the theories of Plato or Aristotle. Others, however, such as Tertullian, rejected Greek philosophy as antithetical to revelation and faith.

Modern Western philosophy

Modern philosophy is generally considered to begin with the work of René Descartes. His work was greatly influenced by questioning from his correspondences with other philosophers. For example, the prodding of Pierre Gassendi and Princess Elizabeth of Bohemia obliged Descartes to try to formulate more cogent replies to the mind-body problem.Medieval philosophy had been concerned primarily with argument from authority, and the analysis of ancient texts using Aristotelian logic. The Renaissance saw an outpouring of new ideas that questioned authority. Roger Bacon (1214–1294?) was one of the first writers to advocate putting authority to the test of experiment and reason. Niccolò Machiavelli (1469–1527) challenged conventional ideas about morality. Francis Bacon (1561–1626) wrote in favor of the methods of science in philosophical discovery.

Analytic and Continental

The late modern period in philosophy, beginning in the late 19th century and lasting to the 1950s, was marked by a developing schism between the "Continental" tradition and the "Analytic" tradition associated with many English-speaking countries.What underlies the analytic tradition, especially the early analytic tradition, is the view (originally defended by Ockham) that much philosophical error arises from misunderstandings generated by language. According to some analytic philosophers, the true meaning of ordinary sentences is "concealed by their grammatical form", and we must translate them into their true form (understood as their logical form) in order to clarify them. The difficulty, so far unresolved, is to determine what the correct logical form must be. Some philosophers (beginning with Frege and Bertrand Russell) have argued that first-order logic shows us the true logical form of ordinary sentences. Other analytic philosophers, such as the late Wittgenstein, rejected the idea of logical form; and this issue of logical form figured prominently in early analytic philosophy. These debates over logical form are no longer as central to analytic philosophy as they used to be, and analytic philosophy now tends to address the full range of philosophical problems with all available philosophical methods. Today analytic philosophy's essence lies more in a style of writing and argumentation (that is, it aims to be clear and rigorous) than in its subject matter or ideas. An emphasis on carefully analyzing language to reveal philosophical errors still remains; but the “analysis” that figures in the name “analytic philosophy” is now just as likely to refer to the analysis of ideas, arguments, social institutions, and presuppositions."Continental" philosophy is most closely identified with the phenomenological movement inaugurated by Edmund Husserl and the various reactions to and modifications of Husserl's work. Phenomenology is primarily a method of investigation. As Husserl conceived it, to investigate phenomenologically is to examine the contents of conscious experience while bracketing all of the assumptions we ordinarily make concerning the existence of objects in the world. He believed that we could arrive at certain knowledge by deducing the necessary features of our conscious experience. Perhaps the most important such feature deduced by Husserl was called intentionality, which denotes the character of consciousness by which it is always directed at some object or other. The phenomenological method is an important alternative to the way that analytic philosophy typically proceeds. Instead of taking linguistic data as the starting point and linguistic analysis as the primary method of philosophy, phenomenology takes conscious experience as the starting point and the detailed analysis of such experience – that is, "phenomenological analysis" – as its method. Some important figures in the analytic tradition such as Wilfrid Sellars and Hector-Neri Castaneda have argued that linguistic analysis is actually a kind of phenomenological investigation because it appeals to our experience as language users to answer philosophical questions. In effect, they have argued that analytic philosophy is but one kind of phenomenology, the implication being that analytic philosophy can ignore the tradition that commences with phenomenology only to its detriment.While Husserl placed great emphasis on consciousness and took up an idealist position motivated largely by a firm distinction between a conscious ego and its objects, the subject-object disinction was deeply critiqued by Husserl's student, Martin Heidegger. Heidegger's 1927 book Being and Time was not only a critique of Husserl, but of a way of thinking that he believed infected the entire Western philosophical tradition of which Husserl was the latest expression. Arguably, Being and Time was the single most revolutionary work of twentieth century philosophy. Though Heidegger radically revised phenomenology, he still considered himself a phenomenologist. With him, phenomenology became existential phenomenology, which focused on producing a "hermeneutics of facticity" – an interpretation of the human condition as lived by real human beings. Heidegger was followed in this effort most famously by Jean-Paul Sartre in his book Being and Nothingness, which carried Heidegger's analysis further and applied it to concrete situations. Maurice Merleau-Ponty critiqued Sartre while still continuing on the path marked by Heidegger's emphasis on our practical engagement with the world as opposed to the Husserlian focus on explicit conscious awareness. The hermeneutical strand of Heidegger's work was developed by Hans-Georg Gadamer in Truth and Method. Together, hermeneutics – the theory of interpretation in the most general sense – and phenomenology constitute the main concerns of continental philosophy. These concerns tend to require a great deal of systematic thinking to make progress in them, and thus continental philosophy tends to look more often at the "big picture" and to deal more directly with everyday human concerns than does analytic philosophy – though like any stereotype, this generalization admits of many exceptions and should not be read to the letter.

Eastern philosophy

Many societies have considered philosophical questions and built philosophical traditions based upon each other's works. Eastern and Middle Eastern philosophical traditions have influenced Western philosophers. Russian, Jewish, Islamic and recently Latin American philosophical traditions have contributed to, or been influenced by, Western philosophy, yet each has retained a distinctive identity.The differences between traditions are often based on their favored historical philosophers, and varying stress on ideas, procedural styles, or written language. The subject matter and dialogues of each can be studied using methods derived from the others, and there are significant commonalities and exchanges between them."Eastern philosophy" refers to the broad traditions that originated or were popular in India, Persia, China, Japan, and to an extent, the Middle East (which overlaps with Western philosophy due to being the origin of the Abrahamic religions).

Indian philosophy
Hindu philosophy constitutes an integral part of the culture of Southern Asia, and is the first of the Dharmic philosophies which were influential throughout the Far East. The great diversity in thought and practice of Hinduism is nurtured by its liberal universalism.The origins of Hindu philosophy are to be traced in Vedic deliberations about the universe and Rta ("universal order"), the first of which was the Rig-Veda, composed in the 2nd millennium BC. Other major texts with philosophical implications include the Upanishads, the Bhagavad Gita, and the Brahma Sutra, from circa 1000 BCE to 500 BCE. The Indian epics Mahabharata and Ramayana also cover Indian philosophy in much depth. At about the same time, the shramana schools, including Jainism and Buddhism, also developed. It is notable that the Vedanta schools of Hindu philosophy are still living traditions today. Hinduism has no known founder or single, authoritative text.Hindu philosophy is traditionally seen through the prism of six different systems (called darshanas in Sanskrit). The six major Astika schools of thought are the Samkhya (enumeration), Yoga (union), Nyaya (logic), Vaisheshika (atomism), Mimamsa (investigation), and Vedanta (culmination of the Vedas) schools. The Vedanta school is further divided into six sub-schools: Advaita (monism/nondualism), VisishtAdvaita (monism of the qualified whole), Dvaita (dualism), Dvaitadvaita (dualism-nondualism), Suddhadvaita, and Achintya Bheda Abheda schools.Buddhist philosophy is a system of beliefs based on the teachings of Siddhartha Gautama, an Indian prince later known as the Buddha, derived from the Sanskrit 'bud', 'to awaken'. Buddhism is a non-theistic religion, one whose tenets are not especially concerned with the existence or nonexistence of a God or gods. The Buddha himself expressly disavowed any special divine status or inspiration, and said that anyone, anywhere could achieve all the insight that he had. The question of God is largely irrelevant in Buddhism, though some sects (notably Tibetan Buddhism) do venerate a number of gods drawn in from local indigenous belief systems.From its inception, Buddhism has had a strong philosophical component. Buddhism is founded on the rejection of certain orthodox Hindu philosophical concepts, in which the Buddha had been instructed by various teachers. Buddhism rejects atheism, theism, monism, and dualism alike. The Buddha criticized all concepts of metaphysical being and non-being, and this critique is inextricable from the founding of Buddhism.Most Buddhist sects believe in karma, a cause-and-effect relationship between all that has been done and all that will be done. Events that occur are held to be the direct result of previous events. One effect of karma is rebirth. At death, the karma from a given life determines the nature of the next life's existence. The ultimate goal of a Buddhist practitioner is to eliminate karma (both good and bad), end the cycle of rebirth and suffering, and attain Nirvana, usually translated as awakening or enlightenment.Jaina philosophy, founded by Mahavira (599-527 BCE), is based upon eternal, universal truths, according to its followers. Over a period of time, these truths may lapse among humanity and then reappear through the teachings of enlightened humans, those who have reached enlightenment or total knowledge (Keval Gnan).Anekantavada is a basic principle of Jainism positing that reality is perceived differently from different points of view, and that no single point of view is completely true. Jain doctrine states that only Kevalis, those who have infinite knowledge, can know the true answer, and that all others would only know a part of the answer. Anekantavada is related to the Western philosophical doctrine of Subjectivism.

Philosophical topics

Metaphysics and epistemology

Rationalism and empiricism

René Descartes, who is often called the father of modern philosophy, proposed that philosophy should begin with a radical skepticism about the possibility of obtaining reliable knowledge. In 1641, in Meditations on First Philosophy, he used this method of doubt in an attempt to establish what knowledge is most certain. He chose as the foundation of his philosophy the famous statement Cogito ergo sum ("I think, therefore I am"). He then attempted to rebuild a system of knowledge based on this single supposedly indubitable fact. His approach became known as a species of rationalism; it attracted such philosophers as Baruch Spinoza, Gottfried Leibniz, and Christian Wolff.In response to the popularity of rationalism, John Locke wrote An Essay Concerning Human Understanding in 1689, developing a form of naturalism and empiricism on roughly scientific principles. Hume's work A Treatise of Human Nature (1739-40) combined empiricism with a spirit of skepticism. Other philosophers who made major contributions to empiricism include Thomas Hobbes and George Berkeley (Bishop Berkeley).During this era, religious ideas played a mixed role in the struggles that preoccupied secular philosophy. Bishop Berkeley's famous idealist refutation of Isaac Newton is a case of an Enlightenment philosopher who drew substantially from religious ideas. Other influential religious thinkers of the time include Blaise Pascal, Joseph Butler, and Jonathan Edwards. Other major writers, such as Jean-Jacques Rousseau and Edmund Burke, took a slightly different path. The restricted interests of many of the philosophers of the time foreshadow the separation and specialization of different areas of philosophy that would occur in the twentieth century.

Kantian philosophy and the rise of idealism
Immanuel Kant wrote his Critique of Pure Reason (1781/1787) in an attempt to reconcile the conflicting approaches of rationalism and empiricism and establish a new groundwork for studying metaphysics. Kant's intention with this work was to look at what we know and then consider what must be true about the way we know it. One major theme was that there are fundamental features of reality that escape our direct knowledge because of the natural limits of the human faculties. Kant's method was modeled on Euclid, though he eventually acknowledged that pure reason was insufficient to discover all truth. Kant's work was continued in the work of Johann Gottlieb Fichte, Friedrich Schelling, and Arthur Schopenhauer.Kant's philosophy, known as transcendental idealism, would later be made more abstract and more general, in the movement known as German idealism, a type of absolute idealism. German idealism rose to popularity with G. W. F. Hegel's publication in 1807 of Phenomenology of Spirit. In that work, Hegel asserts that the aim of philosophy is to spot the contradictions apparent in human experience (which arise, for instance, out of the recognition of the self as both an active, subjective witness and a passive object in the world) and to get rid of these contradictions by making them compatible. Hegel wrote that every thesis creates its own antithesis, and that out of the two arises a synthesis. This process is known as the "Hegelian dialectic". Philosophers in the Hegelian tradition include Ludwig Andreas Feuerbach, Karl Marx, Friedrich Engels, and sometimes the British idealists.

American Pragmatism
The late nineteenth century brought about the rise of a new philosophy in the Americas. Charles Peirce and William James are considered to be the co-founders of loosely allied schools of pragmatism, which introduced what would later be called instrumentalism, the idea that what is important for a good theory is how useful it is, not how well it represents reality. Thinkers in this tradition included John Dewey, George Santayana, and C. I. Lewis. Though not widely recognized under the term "pragmatist", philosophers like Henri Bergson and G. E. Moore shared many of the same foundational assumptions with the pragmatists. Pragmatism has recently been taken in new directions by Richard Rorty and Hilary Putnam.

Phenomenology and hermeneutics
At the same time that the analytic movement was coming to prominence in America and Britain, a separate movement occurred in continental Europe. Under the influence of Franz Brentano, the later Edmund Husserl developed a new method to study human problems in his Logical Investigations (1901) and Ideas (1913). The method, known as phenomenology, was used to examine the details of human experience and consciousness in order to observe the most basic facts of human existence; the examination included not just observations of the way the world appears but observations of one's own thoughts, and when and how they occur. This method was developed further in the work of Martin Heidegger and Maurice Merleau-Ponty.Heidegger expanded the study of phenomenology to elaborate a philosophical hermeneutics. Hermeneutics is a method of interpreting texts by drawing out the meaning of the text in the context it was written in. Heidegger stressed two new elements of philosophical hermeneutics: that the reader brings out the meaning of the text in the present, and that the tools of hermeneutics can be used to interpret more than just texts (e.g. "social text"). [16] Elaborations of philosophical hermeneutics later came from Hans-Georg Gadamer and Paul Ricoeur.

Existentialism

In the mid-twentieth century, existentialism developed in Europe, particularly in France and Germany. The most prominent exponent of existentialism is Jean-Paul Sartre, although existentialist thought received major impetus from the nineteenth century philosophers Søren Kierkegaard and Friedrich Nietzsche, both of whom pre-date existentialism and whose contributions extend beyond existentialist thought.Kierkegaard, a Danish philosopher generally considered the "Father of Existentialism", argued that "truth is subjectivity", meaning that what is most important to an existing being are questions dealing with an individual's inner relationship to existence. Objective truths (e.g. mathematical truths) are important, but detached or observational modes of thought can never truly comprehend human experience. Kierkegaard postulated complex ethico-religious philosophical premises, based in part on the three stages on life's way: the aesthetic, the ethical, and the religious. Nietzsche postulated complex aesthetico-philosophical premises, based in part upon the concept of the will to power.Existentialists sometimes view Nietzsche's thought as characteristic of existentialism, due to the manner in which it places high value in individualism and self-creation, or self-defining.Drawing on these ideas, existentialism rejects the notion of a human essence, instead trying to draw out the ability of each person to live authentically, which is to say that each person is able to define and determine his or her own life. Sartre's expression of existentialism in Being and Nothingness (1943). Other influential existentialists include Albert Camus, Simone de Beauvoir, Maurice Merleau-Ponty and Karl Jaspers. Fyodor Dostoevsky, Franz Kafka, and other literary figures, although not usually considered philosophers, have also contributed greatly to this thought.

Cogito, Ergo Sum

"Cogito, ergo sum" (Latin: "I think, therefore I am") is a philosophical statement by René Descartes, which became a foundational element of Western philosophy. "Cogito ergo sum" is a translation of Descartes' original French statement: "Je pense, donc je suis", which occurs in his Discourse on Method (1637).Although the idea expressed in "cogito ergo sum" is widely attributed to Descartes, many predecessors offer similar arguments—particularly St. Augustine of Hippo in De Civitate Dei (books XI, 26), who also anticipates modern refutations of the concept. (See Principles of Philosophy, §7: "Ac proinde haec cognitio, ego cogito, ergo sum, est omnium prima et certissima etc.").

Introduction

The phrase "cogito ergo sum" is not used in Descartes' most important work, the Meditations on First Philosophy, but the term "the cogito" is (often confusingly) used to refer to an argument from it. Descartes felt that this phrase, which he had used in his earlier Discourse, had been misleading in its implication that he was appealing to an inference, so he changed it to "I am, I exist" (also often called "the first certainty") in order to avoid the term "cogito".At the beginning of the second meditation, having reached what he considers to be the ultimate level of doubt – his argument from the existence of a deceiving god – Descartes examines his beliefs to see if any has survived the doubt. In his belief in his own existence he finds it: it is impossible to doubt that he exists. Even if there were a deceiving god (or an evil demon, the tool he uses to stop himself sliding back into ungrounded beliefs), his belief in his own existence would be secure, for how could he be deceived unless he existed in order to be deceived?"But I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I too do not exist? No: if I convinced myself of something [or thought anything at all] then I certainly existed. But there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So, after considering everything very thoroughly, I must finally conclude that the proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind." (AT VII 25; CSM II 16–17)There are three important notes to keep in mind here. First, he only claims the certainty of his own existence from the first-person point of view — he has not proved the existence of other minds at this point. This is something that has to be thought through by each of us for ourselves, as we follow the course of the meditations. Second, he is not saying that his existence is necessary; he is saying that if he's thinking, then necessarily he exists (see the instantiation principle). Third, this proposition "I am, I exist" is held true not based on a deduction (as mentioned above) nor on empirical induction, but on the clarity and self-evidence of the proposition.Descartes does not use this first certainty, the cogito, as a foundation upon which to build further knowledge; rather, it is the firm ground upon which he can stand as he works to restore his beliefs. As he puts it:"Archimedes used to demand just one firm and immovable point in order to shift the entire earth; so I too can hope for great things if I manage to find just one thing, however slight, that is certain and unshakeable." (AT VII 24; CSM II 16)According to many Descartes specialists including Etienne Gilson, the goal of Descartes in establishing this first truth is to demonstrate the capacity of his criterion -the immediate clarity and distinctiveness of self-evident propositions- to establish true and justified propositions despite having adopted a method of generalized doubt. As a consequence of this demonstration, Descartes considers science and mathematics to be justified to the extent that their proposals are established on a similar immediate clarity, distinctiveness, and self-evidence that present itself to the mind. The originality of Descartes thinking, therefore, is not so much in expressing the cogito -a feat accomplished by other predecessors, as we have seen- but on using the cogito as demonstrating the most fundamental epistemological principle, that science and mathematics are justified by relying on clarity, distinctiveness, and self-evidence.

History of the Quotation

In Descartes' Meditations on First Philosophy, he employs hyperbolic doubt to re-esatblish his existence. Through hyperbolic doubt, he disbands his belief in the existence of everything that has questionable existnce. His purpose is to rebuild the true things in the world. With everything doubted and falisifed, anything recognized as tue will completely be true and there can be no doubt about its validity. Through his method, he derives his first major saying "dubito sum" meaning "I doubt, I am". He recognizes that to be able to doubt, he must exist--within the doubting, there is existence, and vice versa. And as doubting is a form of thinking, "cogito sum" was born.Contrary to popular belief, Descartes never said the phrase "cogito ergo sum." Rather, he said "cogito, sum", which got lost in the translation from French to Latin to English. "Cogito ergo sum" translates as "I think therefore I am" which implies that existence is the effect of the cause of thinking, which is a philosophical fallacy. This jargon is equivillant to making existence a quality with which can be put on an object. [E.g. This ball is red, round, filled with air, and (oh by the way) it exists.] Contrarily, "cogito, sum" translates as "I think, I am" meaning that in doing the thinking, he is also existing at the same time. The thinking and the existing are simultaneous and not causal. Through this point, Descartes has found a point to his Archimedean lever and thus can extrapolate his next major point, the "res cogitans." Which is thus followed by the great deceptor, the existence of God, and the re-establishment of the material world.

Common errors

Some non-philosophers who first come across the cogito attempt to refute it in the following way. "I think, therefore I exist," they argue, can be reversed as "I do not think, therefore I do not exist." They argue that a rock does not think, but it still exists, which disproves Descartes' argument. However, this is the logical fallacy of denying the antecedent. The correct corollary by modus tollens is "I do not exist, therefore I do not think."This fallacy and its prevalence is illustrated by the popular joke:Descartes is sitting in a bar, having a drink. The bartender asks him if he would like another. "I think not," he says, and vanishes.

Criticisms of the cogito

There have been a number of criticisms of the cogito. The first of the two under scrutiny here concerns the nature of the step from "I am thinking" to "I exist". The contention is that this is a syllogistic inference, for it appears to require the extra premise: "Whatever has the property of thinking, exists", and that extra premise must surely have been rejected at an earlier stage of the doubt.It could be argued that "Whatever has the property of thinking, exists" is self-evident, and thus not subject to the method of doubt. This is because the instantiation principle states that: "Whatever has the property F, exists", but within the method of doubt, only the property of thinking is indubitably a property of the meditator. Descartes does not make use of this defence, however; as we have already seen, he responds to the criticism by conceding that there would indeed be an extra premise needed, but denying that the cogito is a syllogism. Jaakko Hintikka offered a non-syllogistic interpretation. "I exist" is immune to Descartes' method of doubt because it is impossible to be mistaken about one's own existence. If we don't exist then we can't be mistaken, so we might as well believe we do.Perhaps a more relevant contention is whether the 'I' to which Descartes refers is justified. In Descartes, The Project of Pure Enquiry Bernard Williams provides a history and full evaluation of this issue. The main objection, as presented by Georg Lichtenberg, is that rather than supposing an entity that is thinking, Descartes should have said: "thinking is occurring." That is, whatever the force of the cogito, Descartes draws too much from it; the existence of a thinking thing, the reference of the "I", is more than the cogito can justify.Williams provides a meticulous and exhaustive examination of this objection. He argues, first, that it is impossible to make sense of "there is thinking" without relativising it to something. It seems at first as though this something needn't be a thinker, the "I", but Williams goes through each of the possibilities, demonstrating that none of them can do the job. He concludes that Descartes is justified in his formulation (though possibly without realising why that was so).

Williams' argument

Whilst the preceding two arguments against the cogito fail, other arguments have been advanced by Williams. He claims, for example, that what we are dealing with when we talk of thought, or when we say "I am thinking", is something conceivable from a third-person perspective; namely objective "thought-events" in the former case, and an objective thinker in the latter.The obvious problem is that, through introspection, or our experience of consciousness, we have no way of moving to conclude the existence of any third-personal fact, verification of which would require a thought necessarily impossible, being, as Descartes is, bound to the evidence of his own consciousness alone.

Parodies

The Ephebian philosophers in Terry Pratchett's Discworld series are often shown interpreting the statement incorrectly, resulting in statements such as "We are therefore we am." and "I think, therefore I do sums."Philosopher Ayn Rand would frequently say "I am, therefore I'll think."In the Monty Python sketch "Bruces' Philosophers Song" from Monty Python Live at the Hollywood Bowl, Descartes is misquoted as saying "I drink, therefore I am."