The term also more specifically refers to an intellectual movement, "The Enlightenment," which is described as being the use of rationality to establish an authoritative ethics, aesthetics, and knowledge. This movement's leaders viewed themselves as a courageous, elite body of intellectuals who were leading the world toward progress, out of a long period of irrationality, superstition, and tyranny which began during a historical period they called the Dark Ages. This movement provided a framework for the American and French Revolutions, as well as the rise of capitalism and the birth of socialism. It is matched by the high baroque era in music, and the neo-classical period in the arts.

Another important movement in 18th century philosophy, closely related to it, was a focus on belief and piety. Often rationalism was used to demonstrate the existence of a supreme being. Piety and belief were an integral part of the exploration of natural philosophy and ethics as well as political theories of the age. At the same time prominent Enlightenment philosophers, such as Voltaire and Jean-Jacques Rousseau questioned and attacked existing institutions of both Church and State.

The 18th century also saw a continued rise of empirical philosophical ideas, and their application to political economy, government and sciences such as physics, chemistry and biology.

It is preceded by the Age of Reason, if thought of as a short period, and by the Renaissance and Reformation if thought of as a long period. It is followed by Romanticism.

Short history of Enlightenment philosophy

The boundaries of the Enlightenment are often thought to cover much of the 17th century as well, though others term the previous era "The Age of Reason." For the present purposes, these two eras are split, however, it is equally acceptable to think of them conjoined together as one long period.

Through the 1500s and half of the 1600s, Europe was wracked by religious wars. When the political situation stabilized, after the Peace of Westphalia and the end of the English Civil War, there was a sharp turn away from the mysticism and belief in individual revelation that was perceived to have driven instability. Instead, according to those that split the two periods, the Age of Reason sought axiomatic philosophy and absolutism as its foundations of knowledge and stability. Epistemology, in the writings of Michel de Montaigne and René Descartes, was based on extreme skepticism, and a quest for the nature of "knowing." The Age of Reason's quest for knowing from axioms would reach its height in pure philosophy with Benedictus de Spinoza and his Ethics, which expounded, a monistic view of the universe where God and Nature were one. This idea would become central to the Enlightenment from Newton through Jefferson.

The Enlightenment was, in many ways, a successor to the ideas of Pascal, Leibniz, Galileo and other philosophers of the previous period. There was a wave of change across European thinking which was exemplified by the natural philosophy of Sir Isaac Newton, mathematical genius and brilliant physicist. The ideas of Newton, his ability to fuse axiomatic proof with physical observation into a coherent system which was easily able to make useful predictions set the tone for much of what would follow in the century after the publication of his Philosophiae Naturalis Principia Mathematica.

But Newton was not alone in the "systematic revolution" in thinking, merely the most visible and famous example. The idea of uniform laws for natural phenomenona mirrored the greater systematization in a variety of studies. If the previous era was the age of reasoning from first principles, the Enlightenment saw itself as looking into the mind of God by studying creation and adducing the basic truths of the world. This view seems over-reaching to the present, where truth is seen as more provisional, but in its time it was a powerful assertion, which turned on its head the basic notions of the sources of legitimacy.

For those that divide the "Age of Reason" from the "Enlightenment," the precipitating figure of Newton offers a specific example of the importance of the difference, because he took empirically observed and codified facts, such as Kepler's planetary motion, and the "opticks" which had explained lenses, and began to create an underlying theory of how they functioned. This shift unified the pure empiricism of such Renaissance figures as Sir Francis Bacon with the axiomatic approach of Descartes. The belief in a comprehensible world, under an orderly Christian God, was to provide much of the impetus for philosophical inquiry. On one hand, religious philosophy focused on the importance of piety, and the majesty and mystery of God's ultimate nature; on the other hand, ideas such as Deism stressed that the world was amenable to human reason, and that the "laws" which governed its behavior were understandable. The analogy of a "clockwork god" or "god the watchmaker" became prevalent, as many in the time period analogized the increasing sophistication of their ability to craft precision machines which kept order, and the universe which seemed to run in an orderly fashion. That navigation and exploration brought a wider variety of circumstances to European notice, and encouraged the search for underlying rules which could be applied to them, is part of the intellectual process at work.

Central to this philosophical tradition was the belief in an objective "truth" which was independent of the observer, but yet expressible in rigorous and human terms. The quest for the expression of this truth would lead to a series of philosophical works which alternately advanced the scepticist position that experience cannot know reality, and the idealist position that the mind was capable of encompassing a reality which lies outside of its direct experience. The realationship between being and perception would be explored by George Berkeley and David Hume, and would eventually be the problem that occupied much of the life's work of Kant.

This focus on law, on the separation of rule from the particulars of behavior or experience, was also essential to the rise of a philosophy which had a much stronger concept of the individual, his rights as being based on other than ancient usage, or tenure, and instead on an intrinsic quality of a person. John Locke wrote his Two Treatises on Government (http://www.lonang.com/exlibris/locke/) to argue that property was not a family right by tenure, but an individual right brought on by mixing labor with the object in question, and securing it from other use. This focus on process and procedure would be honored, at times, in the breach, as England's own "Star Chamber" court would attest to. However, once the concept was established, that there were "natural" rights, as there were "natural" laws - it became the basis for the exploration of what we would now call economics, and political philosophy.

"Enlightenment is man's leaving his self-caused immaturity. Immaturity is the incapacity to use one's own understanding without the guidance of another. Such immaturity is self-caused if its cause is not lack of intelligence, but by lack of determination and courage to use one's intelligence without being guided by another. The motto of enlightenment is therefore: Sapere aude! Have courage to use your own intelligence!"

The Enlightenment began then, from the belief in a rational, orderly and comprehensible universe - and proceeded, in stages, to demand a rational and orderly organization of knowledge and the state, such as found in the idea of Deism. This began from the assertion that law governed both heavenly and human affairs, and that law gave the king his power, rather than the king's power giving force to law. The conception of law as a relationship between individuals, rather than families, came to the fore, and with it the increasing focus on individual liberty as a fundamental reality, given by "Nature and Nature's God," which, in the ideal state, would be as expansive as possible. The Enlightenment created then, the ideas, of liberty, property and rationality which are still recognizable as the basis for most political philosophy even to the present era: that is, of a free individual being most free within the context of a state which provides stability of the laws.

The "long" Enlightenment is seen as beginning out of the Renaissance drive for humanism and empiricism. Building on the natural philosophy that was growing with the application of algebra to the study of nature, and the discoveries brought about by the invention of the microscope and the telescope. There is also an increasingly complex philosophy of the role of the state and its relationship to the individual. The turbulence of religious wars had brought about a desire for balance, order, and unity.

A good paradigm for understanding why there are those that split the Age of Reason from the Enlightenment is the work of Thomas Hobbes and John Locke. Hobbes, a product of the age of reason, systematically pursues and categorizes human emotion, and creates the need for a rigid system to hold back the chaos in his work Leviathan. While John Locke is clearly an intellectual descendant, for him the state of nature is the source of all rights and unity, and the protection of the state is to protect, and not hold back, the state of nature. This fundamental shift, from a rather chaotic and dark view of nature, to a fundamentally orderly view, is an important aspect of the Enlightenment.

A second wave of Enlightenment thinking begins in France with the Encyclopædists. Their ideal was that there is a moral architecture to knowledge. Mixing personal comment with the attempt to codify knowledge, Diderot and D'Alembert sought liberation for the mind in the ability to grasp knowledge.

The Enlightenment was suffused with two competing strains. On one hand there is an intense spirituality, and faith in religion and the church. On the other hand, there is a growing streak of anti-clericalism which mocked the distance between the supposed ideals of the church, and the practice of priests. For Voltaire "Écrasez l'infâme!" would be a battle cry for the ideal of a triumphant, rational, society.

By mid-Century what is regarded by many as the pinnacle of purely Enlightenment thinking was being reached with Voltaire - whose combination of wit, insight, and anger made him the most hailed man of letters since Erasmus. Born Francois Marie Arouet in 1694, he was exiled to England between 1726 and 1729, and there he studied Locke, Newton, and the English Monarchy. Voltaire's ethos was that "Those who can make you believe absurdities can make you commit atrocities" - that if people believed in what is unreasonable, they will do what is unreasonable.

This point is, perhaps, the central point of contention over the Enlightenment: whether the construction of reason and credibility creates, inherently, as many problems as it deals with. From the perspective of many crucial figures of the Enlightenment, credible reports, viewed through the lens of reason annealed knowledge, empirical observation, and knowledge should be compiled into a source which stood as the authoritative one. The countervailing view, held with increasing force by the Romantic movement and its adherents, is that this process is, inherently, corrupted by social convention, and bars "truth" which is unique, individual and immanent from being spelt or spoken.

The Enlightenment balanced then, on the call for "natural" freedom which was good, without "license" which would, in their view, degenerate. Thus the Age of Enlightenment sought reform of Monarchy by laws which were in the best interest of the subjects, and the "enlightened" ordering of society. The idea of enlightened ordering was reflected in the sciences by, for example, Linnaeus' categorization of biology.

In mid-century Germany, the idea of philosophy as a critical discipline began with the work of Lessing and Herder. Both argued that formal unities that underlie language and structure hold deeper meaning than a surface reading, and that philosophy could be a tool for improving the virtue, political and personal, of the individual. This strain of thinking would influence Kant's critiques, as well as subsequent philosophers seeking an apparatus to examine works, beliefs and social organization, and it is particularly notable in the history of later German philosophy.

These ideas became volatile at the point where the idea that natural freedom was more self-ordering than hierarchy, since hierarchy was the social reality. As that social reality repeatedly disappointed the fundamentally optimistic ideal that reform could end disasters, there became a progressively more strident naturalism which would, eventually, lead to the Romantic movement.

Thinkers of the last wave of the Enlightenment - Jean Jacques Rousseau and Immanuel Kant as well as Adam Smith, Thomas Jefferson and the young Johann Wolfgang von Goethe adopted the increasingly biological metaphor of self-organization and evolutionary forces. This represented the impending end of the Enlightenment: which believed that nature, while basically good, was not basically self-ordering - see Voltaire's Candide for an example of why not - but instead had to be ordered by reasoning and maturity. The impending Romantic saw the universe as self-ordering, and that chaos was, in a real sense, the result of an excess of rational imposition on an organic world.

This boundary would produce political results: with increasing force in the 1750s there would be attempts in England, Austria, Prussia and France to "rationalize" the Monarchical system and its laws. When this failed to end wars, there was an increasing drive for revolution or dramatic alteration. The Enlightenment idea of rationality as government found its way to the heart of the American Declaration of Independence, and the Jacobin program of the French Revolution, as well as the American Constitution of 1787.

The French Revolution, in particular, represents the Enlightenment philosophy through a violent and messianic lens, particularly during the brief period of Jacobin dictatorship. The desire for rationality in government lead to the attempt to end the Catholic Church, and indeed Christianity, in France, change the calendar, clock, measuring system, monetary system and legal system along lines suggested by what was seen as an orderly rationality. It also took the ideas of social and economic equality further than any other major state to that time.

But it would be with Napoleon that the Enlightenment and its style would breathe its last, and longest. Napoleon reorganized France into departments, and would fund a host of projects. One example of the Enlightenment idea at work in Revolutionary and Imperial France was the metric system. In a uniform system of weights and measures, based on axiomatic units - the radius of the earth, the weight and thermodynamic properties of water - prices would float based on measurable quantities, rather than price being fixed. It was thought that this would liberate industry from the tyranny of old production laws, and hence from Medieval structure.

Key conflicts within Enlightenment-period philosophy

As with most periods, the individuals present within the Enlightenment were more aware of their differences than their similarities, within the period there were schools of thought which saw themselves as widely divergent, even as later perspective has come to consider them similar.

One key conflict is on the role of theology - during the previous period, there had been the splintering of the Catholic Church, not, as with previous schisms, largely along political control of the papacy, but along doctrinal lines between Catholic and Protestant theologies. This meant that theology itself had become a source of partisan debate, with different schools attempting to create rationales for their viewpoints, which then, in turn, became generally used. Thus philosophers such as Spinoza searched for a metaphysics of ethics, and this trend would influence pietism and eventually transcendental searches such as those by Immanuel Kant.

Religion was linked to another feature which produced a great deal of Enlightenment thought, namely the rise of the Nation State. In medieval and Renaissance periods, the state was restricted by the need to work through a host of intermediaries. This had been a response to poor communication, where localism thrived in return for loyalty to some central organization. With the improvements in transportation, organization, navigation and finally the influx of gold and silver from trade and conquest, the state began to assume more and more authority and power. The response against this was a series of theories on the purpose of, and limits of state power. The Enlightenment saw both the cementing of absolutism and counter-reaction of limitation advocated by a string of philosophers from John Locke forward, who influenced both Voltaire and Jean-Jacques Rousseau.

Within the period of the Enlightenment, these issues began to be explored in the question of what constituted the proper relationship of the citizen to the monarch or the state. The continued growth of the idea that society is a contract between individual and some larger entity, whether society or state, would be advocated by a series of philosophers, including Rousseau, Montesquieu, Hume and ultimately Jefferson. The idea that nationality had a basis beyond mere preference would also be advocated. Philosophers such as Johann Gottfried von Herder reasserted the idea from Greek antiquity that language had a decisive influence on cognition and thought, and that the meaning of a particular book or text was open to deeper exploration based on deeper connections, an idea now called hermeneutics. The original focus of his scholarship was to delve into the meaning in the Bible and in order to gain a deeper understanding of it. These two concepts - of the contractual nature between the state and the citizen, and the reality of the "nation" beyond that contract, would have decisive influence in the development of liberalism, democracy and constitutional government that would follow.

At the same time, the integration of algebraic thinking, acquired from the Islamic world over the previous two centuries, and geometric thinking which had dominated Western mathematics and philosophy since at least Eudoxus, created a scientific and mathematical revolution. Sir Isaac Newton's greatest claim to prominence came from a systematic application of algebra to geometry, and synthesizing a workable calculus which was applicable to scientific problems. The Enlightenment can be aptly thought of as the time where the solar system was truly "discovered": with the accurate calculation of orbits, such as Halley's comet, the discovery of the first planet since antiquity, Uranus by William Herschel, and the calculation of the mass of the Sun using Newton's theory of universal gravitation. The effect that this series of discoveries had on both pragmatic commerce and philosophy cannot be overstated. The excitement of creating a new and orderly vision of the world, as well as the need for a philosophy of science which could encompass the new discoveries would show its fundamental influence in both religious and secular ideas. If Newton could order the cosmos with "natural philosophy," so, it was argued by many, could political philosophy order the body politic.

Within the Enlightment there were two main theories contending to be the basis of that ordering: "divine right" and "natural law." It might seem that divine right would yield absolutist ideas, and that natural law would lead to theories of liberty. The writing of Jacques-Benigne Bossuet (1627-1704) would set the paradigm for the divine right: the universe was ordered by a reasonable God, and therefore his representative on earth had the powers of that God. The orderliness of the cosmos was seen as proof of God, and therefore as proof of the power of monarchy. Natural law, began, not as a reaction against divinity, but instead, as an abstraction: God did not rule arbitrarily, but through natural laws that he enacted on earth. Thomas Hobbes, though an absolutist in government, drew this argument in Leviathan. Once the concept of natural law was invoked, however, it took on a life of its own. If natural law could be used to bolster the position of the monarchy, it could also be used to assert the rights of subjects of that monarch, that if there were natural laws, then there were natural rights associated with them, just as there are rights under man made laws.

What both theories had in common, however, was the need for orderly and comprehensible function of government. The "Enlightened Despotism" of, for example, Catherine the Great of Russia is not based on mystical appeals to authority, but on the pragmatic invocation of state power as necessary to hold back chaotic and anarchic warfare and rebellion. Regularization and standardization were seen as goods, because they allowed the state to reach its power outwards over the entirety of its domain, but also because the liberated people from being entangled in endless local custom, and expanded the sphere of economic and social activity.

Thus rationalization, standardization and the search for fundamental unities would occupy much of the Enlightenment and its arguments over proper methodology and nature of understanding. The culminating efforts of the Enlightenment: for example the economics of Adam Smith, the physical chemistry of Antoine Lavoisier, the idea of evolution pursued by Goethe, the declaration by Jefferson of "inalienable" rights, would, in the end overshadow the idea of "divine right" and direct alteration of the world by the hand of God. It would also be the basis for an overthrow of the idea of completely rational and comprehensible universe, and lead, in turn, to the metaphysics of Hegel and the search for an emotional truth of Romanticism.

Role of the Enlightenment in later philosophy

The Enlightenment's role in modern and post-modern thought

The Enlightenment, an sich occupies a central role in the justification for the movement known as modernism. The neo-classicizing trend in modernism came to see itself as being a period of rationality which was overturning foolishly established traditions, and therefore analogized itself to the Encyclopediasts and other philosophes. A variety of 20th century movements, including liberalism and neo-classicism traced their intellectual heritage back to the "reasonable" past, and away from the "emotionalism" of the 19th century. Geometric order, rigor and reductionism were seen as virtues of the Enlightenment. The modern movement points to reductionism and rationality as crucial aspects of Enlightenment thinking which it is the inheritor of, as opposted to irrationality and emotionalism. In this view, the Enlightenment represents the basis for modern ideas of liberalism against superstition and intolerance. Influential philosophers who have held this view are Jürgen Habermas and Isiah Berlin.

This view asserts that the Enlightenment to being the point where European broke through what historian Peter Gay calls "the sacred circle," where previous dogma circumscribed thinking. The Enlightenment is held, in this view, to be the source of critical ideas, such as the centrality of freedom, democracy and reason as being the primary values of a society. This view argues that the establishment of a contractual basis of rights would lead to the market mechanism and capitalism, the scientific method, religious and racial tolerance, and the organization of states into self-governing republics through democratic means. In this view the tendency of the philosophes in particular to apply rationality to every problem as being the essential change. From this point on, thinkers and writers were held to be free to pursue the truth in whatever form, without the threat of sanction for violating established ideas.

With the end of the Second World War and the rise of post-modernity, these same features came to be regarded as liabilities - excessive specialization, failure to heed traditional wisdom or provide for unintended consequences, and the "romanticization" of Enlightenment figures - such as the Founding Fathers of the United States, prompted a backlash against both "Science" and Enlightenment based dogma in general. Philosophers such as Michel Foucault argued that the "age of reason" had to construct a vision of "unreason" as being demonic and subhuman, and therefore evil and befouling, whence by analogy to argue that rationalism in the modern period is, likewise, a construction. On the opposite side of the coin, the Enlightenment was used as a powerful symbol to argue for the supremacy of rationism and rationalization, and therefore any attack on it is connected to despotism and madness, for example in the writings of Gertrude Himmelfarb and Robert Nozick.

This is not to be confused with the role of specific philosophers or individuals from the Enlightenment, but the use of the term in a broad sense by writers in the present of varying points of view.

Precursors of the Enlightenment

Important figures of the Enlightenment era

Background on Kant 

Immanuel Kant was born in 1724 and died in 1804. He was the son of a poor saddle-maker, but because of his evident intelligence he was sent to university. After receiving a doctoral degree from the Faculty of Philosophy at the University of Konigsberg, he became first a private tutor for families in the area, and then a lecturer at the University of Konigsberg, at which he was to spend the rest of his life teaching. He lectured on a variety of topics including cosmology and anthropology, as well as philosophy.

Kant's major works of philosophy were all written fairly late in his life. The first of these was the Critique of Pure Reason, published in 1781, when Kant was fifty-seven. The Critique of Pure Reason is also known as Kant's first Critique, since it was followed in 1788 by a second Critique, the Critique of Practical Reason and in 1790 by a third Critique, the Critique of Judgment. Each of these books has had a tremendous impact on philosophy concerning its subject manner, which is metaphysics and epistemology for the first Critique, ethics for the second, and aesthetics for the third.

Historical Context

Kant can be regarded as both a participant in the eighteenth century Enlightenment and as a critic of it. He certainly agreed with the French Encyclopedists in celebrating rationality, and in regarding the achievement of his age as that of gradually bringing reason to bear against the forces of superstition, in both the area of science and the realm of religion. (For more about his attitude, see his 1784 essay "An Answer to the Question: What is Enlightenment.") At the same time, however, Kant's philosophy attacks several groups that may be seen as carrying reason too far: metaphysicists who presume to understand God and immortality, scientists who presume their results to describe the intrinsic nature of reality, skeptics who presume to show belief in God, freedom, and immortality to be irrational.

Besides his belief in the importance of rationality, Kant also shared the Enlightenment view that all humans are capable of reason and hence that all are endowed with moral worth. For this reason, he was an enthusiastic supporter of the French Revolution; although saddened by its excesses, Kant regarded the revolution as moving toward a form of government that would recognize the equal worth of all people from a form of government that did not. Although the Critique of Practical Reason is not an explicitly political book, and although Kant was forced even in his political books to refrain from overt support for the revolution for fear of censorship, the following Critique of Practical Reason can be regarded as expressing the view of morality that underlay his revolutionary sentiments.

Philosophical Context

It is difficult to overestimate Kant's influence in philosophy. Even those who reject his explicit theories often use his terms, whether by wondering how it could be possible for something to be "synthetic" (not a matter of meaning) and yet "a priori" (knowable independent of experience), or by asking what is the source of an ethical "imperative." Kant has sometimes been credited for almost single-handedly creating the German philosophical tradition, and it certainly is hard to imagine what Hegel's or Marx's wrings would have looked like without the influence of Kant.

Many current day writers on philosophical ethics have been influenced by Kant. Some accept the categorical imperative as a valid test of moral rightness, but more commonly one will see Kant's linking of morality and autonomy, or his analysis of moral worth as an inner acceptance of the motive of duty, or his insistence that the good is what the moral aims at as opposed to morality being defined by its aim at the good.

The impact of Kant's writing style has arguably also been extensive, on which topic the twentieth century philosophy Walter Kaufmann tartly reports, "Few philosophers since Kant have approximated his genius, but many of his shortcomings are widely shared even today, and to some extant at least this is due to his phenomenal influence." Kant's insights are often masked by his convoluted sentences and unclear technical terms. Fortunately, the second Critique is significantly more accessible than the first, but still the second Critique elicits many conflicting interpretations.

The Critique of Practical Reason can be regarded as the sequel to the Critique of Pure Reason, picking up where that earlier book left off. In the first Critique, Kant divides our judgments in two ways—the a priori (knowable before experience) versus the a posteriori (knowable through experience) and the analytic (true by virtue of meaning) versus the synthetic (true by virtue of the facts). He ultimately concludes, first, that a posteriori judgments are about how things look to us, not about how things intrinsically are, since they are filtered through our experiences, and, second, all synthetic judgments are a posteriori, since we have no access to the world other than through experience.

This second conclusion rules out the possibility of metaphysically proving the existence of God, freedom, and immortality. It does leave open, though, the right to have faith that such things exist in the way the world is in itself, the noumenal realm, since we can never know what is true in that realm. The second Critique will take this further, arguing that the correct understanding of morality requires us to believe in God, freedom, and immortality. As well as continuing from the Critique of Pure Reason, the Critique of Practical Reason lays the grounds for the Metaphysics of Morals, written nine years later in 1797, and which applies the general moral principles of the second Critique to a variety of cases.

The second Critique in some senses can be seen as the opposite of the first Critique. While the main theme of the first Critique is how little we can know about its topic, metaphysics, the second Critique is about how we can know about its topic, morality. Not only that, but some of the first Critique is arguably taken back. We are directly aware of the application of the moral law to us, and through this, we are aware of our freedom, which, it turns out, is awareness of causation from the noumenal world. More than that, not only can we believe in God and immortality, as the first Critique agreed, but it turns out that reason commands belief in them.

In a different sense, though, the second Critique furthers the work of the first. Kant describes himself in the Critique of Pure Reason as having created a revolution to counter Copernicus'. Copernicus humbles man by removing him form the center of the physical universe, but Kant elevates him by presenting the whole phenomenal world of the senses as being created by us and by our senses. In the conclusion of the second Critique, Kant picks up this metaphor again, explaining how he has now shown how the human being lies at the center of the moral universe, and through that universe man connects with the noumenal world.  

Definitions:  

A posteriori  -   The opposite of a priori. Known by experience. 

A priori  -  That which cannot be known without prior experience. For instance, it is a priori that bachelors are unmarried, because one does not need to go check anything in the world to know that this is so. 

Autonomy  -  To be led by a rule, but not one imposed from without. Its opposite is heteronomy, being led from without. Kant understood freedom of the will as autonomy of the will. In the Critique of Practical Reason, he strives to show that the only way to act autonomously is to follow the moral law, and that whenever you follow the moral law, you thereby act autonomously.  

Categorical Imperative  -  A rule for behavior that applies not hypothetically (depending on one's desires) but categorically (which is to say, universally and regardless of one's desires). It's opposite is a hypothetical imperative. Kant believes that only one rule fits this description: act always so that your maxim could hold universally. This rule is often referred to simply as "the categorical imperative." 

Contingent  -   Something that does not necessarily have to be, something that is arbitrary. It is necessary that three and three add up to six. But it is only contingent that Kant was less than than six feet tall.  

Empirical  -   That which can only be known by experience. The empirical world is the phenomenal world.  

Heteronomy  -   Governed by an external rule. The opposite of autonomy.  

Intelligible  -   The intelligible, or noumenal, world is the world as it is in itself. This is opposed by the sensible, or phenomenal world, the world as it appears to us. The fact that the world as it is in itself is not the world that appears to us is the main theme of Kant's Critique of Pure Reason. However, in the Critique of Practical Reason, Kant allows that our feeling for the moral law reveals to us both our noumenal autonomy and the truth of the noumenal postulates of pure practical reason.  

Maxim  -  Rules which underlie one's actions. For Kant, there are two kinds of maxims, the categorical imperative, which is a law of reason, and all other maxims, which cannot be. The categorical imperative itself works by testing the maxim of an act, seeing whether it is universal in scope.

Noumenal  -  See intelligible.  

Phenomenal  -   See intelligible.  

Postulates of Pure Practical Reason  -   Those things that we must postulate in order to follow pure practical reason. Kant places God and immortality in this category. In the Critique of Pure Reason, both God and freedom were regarded as noumenal and thus neither provable nor disprovable. Here, we are given reason to believe in noumenal things, although Kant still insists that we cannot really understand them.  

Pure Reason  -   Reason when it is not influenced by our contingent condition. Pure practical reasoning is an exercise of our decision-making capacities that does not involve our desires. Pure theoretical reasoning is an exercise of our representational capacities not based on our experiences.  

Background on Hobbes and Leviathan 

Thomas Hobbes of Malmsbury was a man who lived with fear. In his autobiography, Hobbes recounted that on the day of his birth in 1588, his mother learned that the Spanish Armada had set sail to attack England. This news so terrified Hobbes's mother that she went into labor prematurely, and thus, writes Hobbes, "fear and I were born twins together." Fear is a significant theme in Hobbes's writing, structuring both his written accounts of his life and the Hobbesian philosophical system.  

Leviathan, Hobbes's most important work and one of the most influential philosophical texts produced during the seventeenth century, was written partly as a response to the fear Hobbes experienced during the political turmoil of the English Civil Wars. In the 1640s, it was clear to Hobbes that Parliament was going to turn against King Charles I, so he fled to France for eleven years, terrified that, as a Royalist, he would be persecuted for his support of the king. Hobbes composed Leviathan while in France, brilliantly articulating the philosophy of political and natural science that he had been developing since the 1630s. Hobbes's masterwork was finally published in 1651, two years after Parliament ordered the beheading of Charles I and took over administration of the English nation in the name of the Commonwealth.

Leviathan's argument for the necessity of absolute sovereignty emerged in the politically unstable years after the Civil Wars, and its publication coincided with that of many Republican treatises seeking to justify the regicide (killing of the king) to the rest of Europe (John Milton's Tenure of Kings and Magistrates is a famous example of these regicide tracts). Not only was the political argument of Leviathan controversial at the time of its publication, but the philosophical method employed by Hobbes to make his claims also scandalized many of his contemporaries--even those writers, such as Robert Filmer (the author of the Royalist tract Patriarcha), who otherwise supported Hobbes's claims for absolute sovereignty.

Hobbes's materialist philosophy was based upon a mechanistic view of the universe, holding that all phenomena were explainable purely in terms of matter and motion, and rejecting concepts such as incorporeal spirits or disembodied souls. Consequently, many critics labeled Hobbes an atheist (although he was not, in the strict sense). Associated with both atheism and the many deliberately terrifying images of Leviathan, Hobbes became known as the "Monster of Malmsbury" and the "Bug-bear of the Nation." In 1666, Hobbes's books were burned at Oxford (where Hobbes had graduated from Magdalen College in 1608), and the resulting conflagration was even blamed in Parliament for having started the Great Fire of London. The chaotic atmosphere of England in the aftermath of the Civil Wars ensured that Hobbes's daring propositions met with a lively reaction.

Hobbes knew that Leviathan would be controversial, for not only did the text advocate restoration of monarchy when the English republic was at its strongest (Oliver Cromwell was not instituted as Lord High Protector until 1653, and the Restoration of Charles II did not occur until 1660), but Hobbes's book also challenged the very basis of philosophical and political knowledge. Hobbes claimed that traditional philosophy had never arrived at irrefutable conclusions, that it had instead offered only useless sophistries and insubstantial rhetoric; he thus called for a reform of philosophy that would enable secure truth--claims with which everyone could agree. Consequently, Hobbesian philosophy would prevent disagreements about the fundamental aspects of human nature, society, and proper government. Furthermore, because Hobbes believed that civil war resulted from disagreements in the philosophical foundations of political knowledge, his plan for a reformed philosophy to end divisiveness would also end the conditions of war. For Hobbes, civil war was the ultimate terror, the definition of fear itself. He thus wanted to reform philosophy in order to reform the nation and thereby vanquish fear.

Earlier in the seventeenth century, Francis Bacon--for whom Hobbes had served as secretary in his youth--had also proposed a reform of philosophy, a reform he called the "Great Instauration." Bacon's program was an inductive philosophy based upon the observation of natural facts ("inductive" reasoning derives general principles from particular instances or facts); the experimental manipulation of nature of Bacon's scheme was very influential for the development of the historical period commonly called the Scientific Revolution, and also formed the backbone of the English Royal Society. Like Hobbes's, Bacon's system rejected traditional philosophical knowledge as untrustworthy, instead embracing nature as the only sure basis for all claims for truth. But Hobbes argued that the experimentalist program was also unsuccessful in providing secure, indisputable knowledge. Hobbes therefore rejected the Baconian system and argued vehemently against it. Hobbes's own deductive scientific philosophy was not experimental--in "deductive" reasoning, a conclusion follows necessarily from the stated premises, rather than being inferred from instances of these premises--but Hobbes maintained that it provided better understanding of the universe and society than both traditional philosophy and experimental science.