Philosophy of the Modern Era

Locke's Theory of Knowledge

John Locke (1632—1704) stands as the apostle of the most moderate and successful of all revolutions—the Revolution of 1688. Its goals were modest yet fully achieved, leaving England without the perceived necessity for another revolution. Locke captures the spirit of this movement, with most of his writings emerging around the year 1688. His principal work in theoretical philosophy, An Essay Concerning Human Understanding, was completed in 1687 and published in 1690. His First Letter on Toleration was initially published in Latin in 1689 in the Netherlands, the country where Locke prudently sought refuge in 1683. Two subsequent letters on toleration were published in 1690 and 1692. Permission for the publication of his two Treatises of Government was granted in 1689, shortly after which they came to light. His book Thoughts Concerning Education was published in 1693. Despite his long life, all of his influential works are confined to a brief period—from 1687 to 1693. Successful revolutions inspire those who believe in them.

Locke's father was a Puritan who fought on the side of Parliament. During Cromwell's rule, while Locke was at Oxford University, scholastic philosophy still prevailed there; he held an aversion to both scholasticism and the fanaticism of the Independents. René Descartes greatly influenced him. Locke became a physician, patroned by Lord Shaftesbury—Dryden’s Ahithophel. When Shaftesbury fell from grace in 1683, Locke fled with him to the Netherlands, where he remained until the revolution. After the revolution, with the exception of a few years spent in the Ministry of Trade, he dedicated his life to literary work and the countless discussions arising from his writings.

In the years leading up to the Revolution of 1688, during which Locke could not risk either theoretical or practical involvement in English politics, he composed his Essay Concerning Human Understanding. This pivotal work brought him the most acclaim, and yet his influence on political philosophy has been so profound and enduring that he can be regarded as the founder of philosophical liberalism, just as he is of empiricism in epistemology.

Locke is the most fortunate of all philosophers. He completed his theoretical philosophy just as governance in his country fell into the hands of those who shared his political views. In the following years, the most vigorous and influential politicians and philosophers supported, both in practice and theory, the views he espoused. His political theories, later developed by Montesquieu, are reflected in the American Constitution and are applicable wherever disputes arise between the president and Congress. His theories underpinned the British Constitution until about fifty years ago, and the same holds true for the French Constitution adopted in 1871.

In 18th-century France, Locke's considerable influence initially stemmed from Voltaire, who, as a young man, spent time in England and advocated English ideas to his compatriots in his Philosophical Letters. He was followed by philosophers and moderate reformers; meanwhile, the more radical revolutionaries aligned themselves with Rousseau. Whether rightly or wrongly, Locke's French followers believed in a close connection between his theory of knowledge and his political views.

In England, this connection is less apparent. Of Locke's two most renowned followers, Berkeley did not play a significant role in politics, while Hume belonged to the Tory party and expressed his reactionary views in his History of England. However, after Kant, as German idealism began to influence English thought, a connection between philosophy and politics re-emerged: philosophers following German idealists were primarily conservatives, while followers of Bentham, a radical, remained faithful to Locke's traditions. Yet this relationship was not constant; T.H. Green, for instance, was both a liberal and an idealist.

Not only Locke's correct views but even his practical errors proved beneficial. Consider, for example, his theory of primary and secondary qualities. Primary qualities include those inseparable from the body: density, extension, figure, motion or rest, and number. Secondary qualities encompass everything else: color, sound, smell, and so forth. He asserts that primary qualities exist in bodies, while secondary qualities, conversely, exist only in perceptions. Without the eye, there would be no colors; without the ear, there would be no sounds, and so on. There is substantial evidence supporting Locke's views regarding secondary qualities: jaundice, blue glasses, and the like. However, Berkeley pointed out that similar arguments apply to primary qualities. Since Berkeley's time, Locke's dualism on this matter has become philosophically outdated. Nonetheless, in practical physics, it has dominated until the advent of contemporary quantum theory. It was not only explicitly or implicitly accepted by physicists but also proved useful as a source of many significant discoveries. The theory that the physical world consists solely of moving matter served as the foundation for accepted theories of sound, heat, light, and electricity. Pragmatically, the theory has been useful, however erroneous it may be theoretically. This exemplifies a typical doctrine of Locke.

Locke's philosophy, as evident from the study of An Essay Concerning Human Understanding, is imbued with certain merits and specific shortcomings. Both are equally beneficial; the shortcomings are only theoretically problematic. Locke is always prudent and is more inclined to sacrifice logic than to appear paradoxical. He proclaims general principles that, as any reader can easily imagine, could lead to strange consequences; yet whenever such curious implications seem poised to emerge, Locke tactfully refrains from drawing them out. This logic may irritate but serves as proof of sound judgment for practical individuals. Since the world is what it is, it is clear that a correct conclusion drawn from true premises cannot lead to errors; however, the premises may be close enough to the truth as required theoretically and yet lead to practically absurd conclusions. Thus, there is justification for common sense in philosophy, but only in that it demonstrates that our theoretical propositions cannot be entirely correct until their consequences are verified by common sense, which proves irresistible. The theorist might argue that common sense is no more infallible than logic. Yet this objection, made by Berkeley and Hume, would be entirely foreign to Locke's intellectual character.

A distinctive feature of Locke, which extends to all liberal thought, is the absence of dogmatism. The belief in our own existence, the existence of God, and the truth of mathematics—these are the few undeniable truths that Locke inherited from his predecessors. Yet, no matter how his theory diverges from those of his predecessors, he concludes that truth is elusive and that a rational person will hold to their views while retaining a degree of doubt. This mindset is evidently linked to religious tolerance, the success of parliamentary democracy, laissez-faire, and the entire system of liberal attitudes. Though Locke is a deeply religious man, sincerely believing in Christianity and accepting revelation as a source of knowledge, he nonetheless subjects revelation to the scrutiny of reason. At one point, he asserts, “The simple testimony of revelation is the highest certainty,” but in another, he states, “Reason must judge revelation.” Thus, ultimately, reason prevails.

The chapter titled "On Enthusiasm" is particularly revealing in this context. At that time, "enthusiasm" did not carry the same meaning as it does today; it referred to faith in the personal revelations of religious leaders or their followers. This is a characteristic feature of sects that suffered defeat during the Restoration. When there exist numerous such personal revelations, each incompatible with the others, truth— or what is perceived as truth—becomes purely individual and loses its social character. The love of truth, which Locke deems essential, stands in stark contrast to the love for particular theories accepted as truth. An infallible sign of love for truth, he asserts, is "not to uphold any proposition with greater confidence than the evidence upon which it is built permits." He claims that the inclination to prescribe shows an inability to love truth. "Enthusiasm, by excluding reason, seeks to establish revelation without its aid. But in reality, it simultaneously removes both reason and revelation, replacing them with baseless fantasies of the human imagination." Those afflicted by melancholy or vanity are likely "convinced of direct communication with the Divine." Consequently, the most varied actions and views receive divine sanction, which encourages "human laziness, ignorance, and vanity." He concludes the chapter with the aphorism that "reason must judge revelation."

What Locke means by the term "reason" can only be discerned through a comprehensive understanding of his entire work. Although there is a chapter titled "On Reason," it primarily aims to demonstrate that reason is not comprised of syllogistic reasoning. The essence of the chapter is summarized in the assertion that "the Lord God was not so miserly towards humanity as to create them merely as bipedal beings and leave it to Aristotle to make them reasonable." For Locke, reason has two components: the first is the establishment of what pertains to things about which we possess certain knowledge; the second involves the examination of propositions that are wise to adopt in practice, even if they are merely probable and uncertain. "There are two grounds of probability," he states, "the agreement with our own experience or the confirmation by the experiences of others." The Siamese king, he notes, ceased to believe what Europeans told him when they mentioned ice.

In the chapter "On Degrees of Agreement," he asserts that the degree of agreement regarding any proposition depends on the grounds of probability supporting it. After indicating that we must often act based on probability that approaches certainty, he states that the correct application of this consideration "lies in mercy and leniency toward one another." Given that most people, if not all, inevitably hold differing opinions without possessing reliable and incontrovertible evidence of their truth, to retreat and abandon one's previous convictions immediately after an argument that cannot be instantly countered or shown to be deficient invites grave accusations of ignorance, frivolity, or folly. Thus, I believe that amid differing opinions, all people should maintain peace and fulfill the common duty of humanity and friendliness. It would be unreasonable to expect anyone to willingly and obligingly relinquish their opinion and accept ours with blind submission to an authority that reason does not recognize. For, no matter how often reason may err, it can only be guided by its own reasoning and cannot blindly submit to the will and dictates of others. If a person you wish to sway is the type who first studies a matter and then agrees, you must give them the opportunity to reconsider everything at their leisure so that, recalling what has slipped from their mind, they can examine all the particulars to see where the advantage lies. And if this person does not find our arguments sufficiently compelling to reinvest themselves in such endeavors, then we often act similarly in such cases. We would be offended if others attempted to dictate to us what questions we should study. Moreover, if a person accepts beliefs on faith, how can we imagine they will renounce those convictions that time and habit have so entrenched in their minds that they regard them as self-evident, possessing indisputable validity, or view them as impressions received directly from the Divine or from individuals sent by Him? How can we expect, I reiterate, for opinions thus solidified to yield to the arguments or authority of an outsider or adversary, especially in the presence of suspicion of vested interest or malice, as is always the case when people feel mistreated? We would do well to be forgiving of our ignorance and strive to remedy it by gently and politely enlightening others, avoiding immediately treating them as stubborn or corrupt individuals merely because they are reluctant to abandon their opinions in favor of ours or, at the very least, those opinions we would like to impose upon them, while it is far more likely that we are equally obstinate in regard to accepting some of their views. For, where is the individual who possesses unquestionable certainty about the truth of all that they condemn? Who can claim to have thoroughly studied all their own and others' opinions? Given our instability in actions and our blindness, the necessity to believe without knowledge, often even on very weak foundations, should compel us to be more active and diligent in seeking our own enlightenment rather than in compelling others… And there is reason to believe that if people were better educated themselves, they would be less intrusive.

Thus far, I have dealt only with the latter chapters of the "Essay," in which Locke presents his views on morality, derived from his earlier theoretical inquiries into the nature and limits of human knowledge. Now, it is essential to consider what he intended to convey regarding this strictly philosophical question.

Locke generally holds metaphysicians in disdain. Regarding some speculations of Leibniz, he writes to a friend, "Both you and I have had our fill of such trifles." He considers the concept of substance, which was predominant in metaphysics during his time, to be vague and unhelpful, yet he does not dare to entirely reject it. Locke allows for the validity of metaphysical arguments for the existence of God, but he does not dwell on them, and it seems he feels somewhat uneasy discussing them. Whenever Locke articulates new ideas rather than merely reiterating traditional ones, his thought remains confined to specific concrete issues, rather than resorting to broad abstractions. His philosophy unfolds gradually, akin to scientific inquiry, and is not a monumental edifice like the great continental systems of the seventeenth century.

Locke may be regarded as the founder of empiricism—the doctrine asserting that all our knowledge (perhaps excluding logic and mathematics) is derived from experience. Accordingly, the first book of the "Essay," in opposition to Plato, Descartes, and the scholastics, asserts that there are no innate ideas or principles. In the second book, he endeavors to demonstrate in detail how various types of ideas arise from experience. Rejecting innate ideas, he states: "Suppose the mind is, so to speak, a blank sheet of paper without any marks or ideas. But how does it acquire them? From where does it obtain that extensive stock, which the active and boundless human imagination has painted with almost infinite variety? Where does it derive all the material for reasoning and knowledge? To this, I answer in a single word: from experience. All our knowledge is based on experience; from it, it ultimately originates."

Our ideas are derived from two sources: a) sensations and b) perceptions of the workings of our own minds, which can be termed "internal sense." Since we can think only through ideas and since all ideas arise from experience, it is evident that none of our knowledge can precede experience.

Perception, he asserts, is “the first step towards knowledge, the path through which all material comes to it.” To the modern individual, this statement may seem nearly a truism, as it has become ingrained in the consciousness of the educated, at least in English-speaking countries. Yet, in Locke's time, it was widely believed that the mind possessed a priori knowledge of all kinds of things, and the theory proposing the complete dependence of knowledge on perception, put forth by Locke, was both new and revolutionary. In Theaetetus, Plato attempted to reject the identity of knowledge and perception, and since his era, nearly all philosophers, including Descartes and Leibniz, taught that many of our most valuable forms of knowledge do not derive from experience. Thus, Locke's all-encompassing empiricism represented a bold innovation.

The third book of An Essay Concerning Human Understanding addresses the examination of words and primarily seeks to demonstrate that what metaphysicians represent as knowledge of the world is purely verbal knowledge. In Chapter III, “Of General Terms,” Locke adopts an extremely nominalistic stance on universals. All things that exist are singular, yet we can form a general idea, such as “man,” which applies to many singular entities, and we can bestow names upon these general ideas. Their general nature lies solely in the fact that they are applicable or can be applied to a multitude of singular things; in and of themselves, as ideas in our minds, they are as singular as anything that exists.

Chapter VI of the third book, “Of Names of Substances,” aims to refute the scholastic doctrine of essence. Things may possess a real essence, which is their physical organization, but this is largely unknown to us and is not the “essence” of which the scholastics speak. The essence, as we can know it, is purely verbal; it consists simply in the definition of the general term. For example, the dispute over whether the essence of a body is merely extension or extension plus density is a dispute about words: we can define the word “body” in any way we choose, and there is no harm in this as long as we adhere to our definition. Distinct species are not a fact of nature but rather a fact of language; they represent “a distinct complex of ideas, with distinct names assigned to them.” While various things do indeed exist in nature, the differences manifest themselves as continuous gradations: “The boundaries of species, by which people distinguish them, are created by humans.” He cites examples of mutants, regarding whom it remains uncertain whether they were truly human. This perspective was not widely accepted until Darwin, with his theory of evolution, persuaded people of the existence of gradual changes. Only those unsatisfied with the teachings of the scholastics could grasp how much metaphysical clutter this theory swept away.

Both empiricism and idealism have confronted a problem that philosophy has yet to resolve satisfactorily. This problem lies in elucidating how we come to know other entities that differ from ourselves and what actions pertain to our own minds. Locke addresses this issue, but what he articulates proves wholly unsatisfactory. At one point, he states: “Since the mind, in all its thoughts and reasonings, has no immediate object other than its own ideas, which it considers or can consider, it is evident that our knowledge pertains solely to them.” Again, he posits: “Knowledge is the perception of the agreement or disagreement of two ideas.” From this, it seemingly follows that we cannot know of the existence of other people or the physical world, as they, if they exist, are not merely ideas in my mind. Each of us, in terms of knowledge, must consequently close in upon ourselves and renounce any contact with the external world.

However, this is a paradox, and Locke does not acknowledge paradoxes. Accordingly, in another chapter, he proposes a different theory that is entirely incompatible with the previous one. We possess, he asserts, three types of knowledge of real existence. Our knowledge of our own existence is intuitive, our knowledge of the existence of God is demonstrative, and our knowledge of things given to the senses is sensory.

In the next chapter, he begins to understand their incompatibility to a certain extent. He suggests that one might say: “If knowledge truly consists only in the perception of the agreement or disagreement of our own ideas, then the visions of the enthusiast and the reasonings of the sane person would be equally valid.” He responds: “Not so, where ideas correspond to things.” He continues to assert that all simple ideas must correspond to things, as the mind, according to the aforementioned, cannot itself form any simple ideas: all of them are “the product of things acting upon the mind.” As for complex ideas of substances, “all our complex ideas must be such and only such as composed of those simple ideas that have been revealed as coexisting in nature.” Moreover, we can gain knowledge only through 1) intuition, 2) reasoning, examining the agreement or disagreement of two ideas, and 3) sensation, which perceives the existence of individual things.

In all of this, Locke presupposes that certain mental phenomena, which he refers to as sensations, are caused by external factors and that these causes, at least to some degree and in certain respects, resemble the sensations they produce. But how, given the principles of empiricism, does this become known? We experience sensations but not their causes; the effects of sensations would be precisely the same as if our sensations arose spontaneously. The belief that sensations have causes, and even more so the belief that they resemble their causes, is a conviction that, if held, must be maintained on grounds entirely independent of experience. The view that “knowledge is the perception of the agreement or disagreement of two ideas” is attributed to Locke; however, to escape the paradoxes this view generates, he can only resort to means so contradictory that only Locke’s unyielding adherence to common sense allowed him to remain blind to this.

This difficulty continues to trouble supporters of empiricism to this day. Hume overcame it by discarding the assumption that sensations have external causes, but even he maintained this assumption whenever he forgot his own principle, which happened very frequently. His primary principle, “no ideas without prior impressions,” which he inherited from Locke, remains credible as long as we conceive of impressions as something evoked by external causes, to which the very word “impression” inevitably directs our thoughts. And when Hume’s reasonings become somewhat coherent, they also become extraordinarily paradoxical.

No one has yet succeeded in formulating a philosophy that is simultaneously trustworthy and consistent. Locke sought credibility and achieved it at the expense of consistency. Most great philosophers have done the opposite. A philosophy that is not consistent cannot be wholly true; however, a philosophy that is consistent can very easily turn out to be entirely false. The most fruitful philosophical systems have contained glaring contradictions, but precisely for this reason, they have been partially true. There is no reason to believe that a non-contradictory system contains more truth than one, like Locke's, which is evidently more or less incorrect.

The ethical theories of Locke are intriguing both in their own right and as a precursor to Bentham's ideas. When I refer to his ethical theories, I am not alluding to his moral inclinations as a practitioner but rather to his overarching theories regarding human actions and the moral ought. Like Bentham, Locke was an exceptionally benevolent individual who believed that each person (including himself) should be driven solely by the desire for their own happiness or pleasure. Several quotes elucidate this position:

"Things are deemed good or evil exclusively in relation to pleasure and pain. We call that good which can cause or enhance pleasure and diminish suffering."

"What motivates desire? I respond: happiness, and only happiness."

"Happiness, in its entirety, is the highest pleasure to which we are capable."

"The necessity of pursuing true happiness is the foundation of all freedom."

"The preference of vice over virtue is a manifest false judgment."

"Mastery over one's passions is the true development of freedom."

Evidently, the last assertion hinges on the theory of reward and punishment in the afterlife. God has bestowed certain moral rules; those who adhere to them shall ascend to heaven, while those who choose to transgress risk descending into hell. Thus, a person wisely indulging in pleasures will be deemed virtuous. With the decline of faith in the notion that sin leads to damnation, it has become more challenging to advance purely selfish arguments in favor of a virtuous life. Bentham, a freethinker, replaced God with the human legislator: establishing harmony between societal and personal interests became the purview of laws and social institutions, compelling each individual in their pursuit of personal happiness to contribute to the common good. Yet, this is less satisfying than the reconciliation of public and personal interests facilitated by the means of heaven and hell, for legislators are not always wise and virtuous, and human governments lack omniscience.

Locke is compelled to acknowledge the evident truth that people do not always act in ways that, according to rational calculations, would yield them the maximum pleasures. We value present pleasures more than future ones and pleasures of the near future more than those of the distant future. One might assert (though Locke does not) that the degree of interest is a quantitative measure of the general devaluation of future pleasures. If the prospect of spending one thousand pounds in the coming year were as delightful as the thought of spending them today, I would have no reason to regret deferring pleasure. Locke conceded that devout believers often commit sins that they believe threaten to cast them into hell. We all know individuals who postpone a visit to the dentist longer than they would if they were rationally striving for pleasure. Therefore, even if our motivations are driven by pleasure or the desire to avoid suffering, it must be added that pleasures lose their allure and suffering loses its sharpness in proportion to their distance from the present.

Since, according to Locke, selfish and common interests align only in the long run, it is imperative for individuals to be guided by their ultimate interests as much as possible. In other words, people must exercise prudence. Prudence is the only virtue that ought to be preached, as every transgression against virtue is a deficiency in prudence. The emphasis on prudence is a hallmark of liberalism. This is linked to the rise of capitalism, where the prudent have become wealthy, while the imprudent have become or remained poor. It is also connected to certain forms of Protestant piety: virtue with an eye toward heaven psychologically resembles thrift with an eye toward a commercial bank.

The belief in harmony between personal and societal interests is a defining feature of liberalism and has long outlived the theological foundations upon which it rested in Locke's thought.

Locke asserts that freedom is grounded in the necessity of achieving true happiness and in mastering our passions. He derives this view from his theory that personal and public interests ultimately coincide, though not necessarily at every individual moment. From this theory, it follows that a given community of citizens, equally pious and prudent, will act with the freedom to attain the common good. There will be no need for them to be restrained by human laws, as divine laws will suffice. Until now, a virtuous person tempted to become a robber tells himself: "I might evade human judgment, but I cannot escape punishment from the Divine Judge." Consequently, he will renounce his wicked plans and live as virtuously as if he were certain that the police might catch him. Therefore, legal freedom is entirely possible only where prudence and piety coincide and are widely disseminated; elsewhere, the constraints imposed by criminal law are obligatory.

Locke repeatedly asserts that morality is subject to justification, yet he does not develop this idea as fully as one might wish. Here is the most significant passage in this regard:

"Morality can be proven through reasoning. The idea of a Supreme Being of infinite power, goodness, and wisdom, from whom we are created and upon whom we depend, and the idea of man as a rational and understanding being, with the clarity these ideas convey, could, in my view, upon proper examination and adherence, provide a basis for our duties and rules of conduct, capable of placing morality among the demonstrable sciences; and I have no doubt that it would be possible to establish measures of good and evil based on self-evident propositions through deductions as necessary and indisputable as those in mathematics, establishing them for anyone who engages in morality with the same impartiality and attention as one would in mathematical sciences. The relationship of other modes can be perceived with the same certainty as the relationship of modes of number and extension; and I see no reason why other modes could not be demonstrable if one were to consider the proper methods of study and trace their correspondence or non-correspondence. The proposition 'Where there is no property, there is no injustice' is as certain as any proof in Euclid: for if the idea of property is a right to any thing, and the idea designated by the term 'injustice' is an encroachment upon or violation of that right, it is clear that as long as these ideas are established in this manner and linked to the specified terms, I can ascertain the truth of this proposition with the same certainty as that of the fact that the three angles of a triangle equal two right angles. Another example: 'No state grants complete freedom.' If the idea of a state is the arrangement of society according to specific rules or laws that require compliance, and the idea of complete freedom consists for each in doing as they please, then I can be confident in the truth of this proposition no less than in the truth of any proposition in mathematics."

This passage presents a conundrum, for it seemingly places the rules of morality under the auspices of Divine predestination while simultaneously suggesting through its examples that moral rules are analytic in nature. I believe that Locke, in truth, posited that one aspect of ethics is analytic while another is contingent upon Divine decrees. However, another perplexity arises from the fact that the examples he provides do not appear to constitute ethical propositions at all.

There is also another difficulty that one might wish to contemplate. Theologians generally assert that Divine predestination is not arbitrary but stems from His goodness and wisdom. This necessitates the existence of some conception of goodness that precedes Divine decrees— a notion that leads God to enact this particular predestination rather than another. From Locke’s perspective, it is impossible to elucidate what this notion might be. He merely states that the prudent man will act in such and such a manner because otherwise, God will punish him. Yet, he leaves us entirely in the dark as to why punishment should be meted out for certain actions rather than others. Locke’s ethical theory, indeed, cannot be justified. Apart from the unsettling nature of a system that regards prudence as the sole virtue, there are other, less emotive objections to his theory.

First, to assert that individuals desire only pleasures is to place the cart before the horse. Whatever I may wish for, I will feel pleasure upon satisfying that desire; yet pleasure is grounded in desire, not vice versa. One can, as is the case with masochists, desire suffering; in this scenario, there remains pleasure in the satisfaction of desires, albeit intertwined with its opposite. Even according to Locke’s own theory, people do not desire pleasure as such, since immediate pleasures are more desirable than those that are remote. If morality is to be derived from the psychology of desire, as Locke and his followers attempt, then there can be no grounds for objecting to the disregard of distant pleasures or for preaching prudence as a moral duty. His argument can be succinctly summarized as follows: “We desire only pleasures. Yet, in fact, many individuals desire not pleasure as such, but rather immediate pleasures. This contradicts our theory that they desire pleasure per se, therefore it is immoral.” Almost all philosophers, in their ethical systems, first propose a false theory and then argue that the evil lies in acting in a manner that proves the theory false. Such a situation could not arise if the theory were true. Locke’s theory exemplifies this kind of fallacy.