John Locke's An Essay Concerning Human Understanding is a classic statement of empiricist epistemology. Written in a straightforward, uncomplicated style, the Essay attempts nothing less than a fundamental account of human knowledgeits origin in our ideas and application to our lives, its methodical progress and inescapable limitations. Even three centuries later, Locke's patient, insightful, and honest reflections on these issues continue to merit the careful study that this guide is intended to encourage.
Locke prefaced his masterwork with a rhetorically understated "Epistle to the Reader." His awareness of the need for a systematic investigation of the human understanding first arose in the context of a friendly but unproductive discussion of other issues. (According to another of the participants in that meeting, they included "the Principles of morality, and reveald Religion.") Although he drafted a preliminary account that dealt with many of the central themes of the Essay as early as 1671, Locke expanded his comments repeatedly before publishing the book nearly twenty years later and continued to supplement them with additional material he prepared for four further editions. Claiming only to be an "Under-Labourer" whose task is to prepare the way for the "Master-Builders" of science, he encouraged ordinary readers to rely upon their own capacity for judgment rather than to accept the dictates of intellectual fashion. [Essay Epistle]
In the daily course of ordinary activity, everyone is inclined to rely upon a set of simple guidelines for living, and laziness or pride may encourage us to accept dearly held convictions without ever embarking on a careful examination of their truth. But this is a dangerous course. Locke pointed out that blind acceptance of "borrowed Principles"the confident pronouncements of putative cultural authorities regarding crucial elements of human lifeoften leaves us vulnerable to their imposition of absurd doctrines under the guise of an innate divine inscription. [Essay I iii 24-26] Our best defense against this fate is to engage in independent thinking, which properly begins with a careful examinination of the function and limits of our discursive capacities.
Attention to specific issues at hand often leads us to overlook the function of the most noble of our faculties, but Locke believed that the operations of the human understanding are familiar to us all. We employ ourselves in thinking, deciding, doing, and knowing all the time. What we require is not a detailed scientific explanation of the nature of the human mind, but rather a functional account of its operations in practice. For that purpose, Locke supposed, we must pursue the "Historical, plain Method" of observing ourselves in the process of thinking and acting. With respect to each significant area of human knowledge, we must ask ourselves: where does it come from, how reliable is it, and how broadly does it extend? [Essay I i 1-2]
The last of these questions is arguably most to the point. Locke realized early on in his epistemological reflections that skeptical doubts often arise from unreasonable expectations about the degree of certainty it is possible for us to attain. [King, p. 107] Academic philosophers have contributed to the problem by demanding demonstrative certainty of the speculative truth even in instances where we are unlikely to be able to achieve it. But their demands for excessive precision in philosophical language lead only to pointless wrangling over the meanings of their terms, on Locke's view. The simple truth is that we can't be certain about everything, and it would be counter-productive to try to expand our knowledge beyond its natural limits. Since we are not capable of knowing everything, contentment with our condition requires a willingness not to reach beyond the limitations of our cognitive capacities. Our intellectual energy would be most efficiently employed were we to avoid intractable disputes over matters beyond our ken and rely instead upon our "Satisfaction in a quiet and secure Possession of Truths, that most concern'd us." [Essay I i 7] In ordinary life, we know what we need to know, and expecting more than that would only lead us to despair.
After all, Locke argued, we do have what we need most. The practical conduct of human life doesn't depend upon achieving speculative certainty about the inner workings of the natural world or acquiring detailed information about our own natures. It will be enough if we can secure "the Conveniences of Life" and recognize what we ought to do.
How short soever their Knowledge may come of an universal, or perfect Comprehension of whatsoever is, it yet secures their great Concernments, that they have Light enough to lead them to the Knowledge of their Maker, and the sight of their own Duties. Men may find Matter sufficient to busy their Heads, and employ their Hands with Variety, Delight, and Satisfaction; if they will not boldly quarrel with their own Constitution, and throw away the Blessings their Hands are fill'd with, because they are not big enough to grasp every thing. [Essay I i 5]The pursuit of happinessthe genuine business of human life, on Locke's viewdemands only that religion, morality, and science be established to a degree that permits practical progress.
Even with respect to such vital matters, Locke supposed, our knowledge is often limited. The testimony of our senses, together with a natural inclination to seek pleasure and avoid pain, guides much of our daily conduct even though sensitive knowledge cannot offer demonstrative certainty about the existence of an external world. [Essay IV xi 8-10] It would be foolish indeed to refuse to eat simply because God has not granted us speculative certainty regarding the nutritional efficacy of food. Divine provision for the practical needs of human life is expressed more economically:
So in the greatest part of our Concernment, he has afforded us only the twilight, as I may so say, of Probability, suitable, I presume, to that State of Mediocrity and Probationership, he has been pleased to place us in here. [Essay IV xiv 2]The pace of ordinary life commonly requires all of us to act quickly, on the basis of little more than our fallible memory of the merely probable evidence in favor of this course of action, Locke supposed, but awareness of this common reliance on "our mutual Ignorance" appropriately motivates broad toleration of the diversity of opinions and practices to which others may adhere. [Essay IV xvi 3-4]
The great theme of the Essay, then, is that we ought not to expect to achieve knowledge beyond the relatively narrow confines of what is necessary or, at least, useful for the practical conduct of human life. Although speculative knowledge of the essences of God, human beings, and material things exceeds the capacity of our cognitive faculties, according to Locke, we have no grounds for complaint. Observation of the causal regularities in nature enables us to secure our survival and comfort, "ease, safety, and delight," during this life. What is more, evaluation of our moral conduct in the light of our accountability to God for the actions we perform provides amply for our hope of a better existence beyond this life. Limited though it may be, Locke supposed, the human capacity for knowledge is sufficient for our happiness here and hereafter, and since that is that is our primary concern, it would be pointless to demand that our faculties reach any further. [King, pp. 86-92]
A year before the first edition was published, Locke wrote an "Abstract of the Essay." Translated into French by his friend Jean le Clerc, this document was published in the Bibliothèque Universelle in 1688, giving the European intellectual community a full preview of the work to come. This presentation of the central themes indicates what Locke himself regarded as his most significant contributions to the subject.
After a mere mention of the polemic against innate ideas, Locke explained his own belief that all human thought originates in the simple ideas of sensation and reflection. He devoted particular attention to the primary/secondary quality distinction and to the acquisition of simple ideas of space, time, number, pleasure, and pain. Then he outlined the account of our formation of crucial complex ideas, including those of substances, mixed modes, and relations. [King, pp. 365-378]
Noting his own belated discovery of the vital importance of language, Locke offered a basic statement of his own theory of language, with special attention to the relation between general terms and abstract ideas. Drawing the distinction between civil and philosophical uses of language, he pointed out that difficulties in communication result both from the natural imperfections of language and from its deliberate misuse. [King, pp. 378-388]
Finally, Locke defined knowledge and distinguished its several types, each of which is subject to strict limitations. Arguing in some detail against the common inclination to rely upon supposedly self-evident principles, Locke proposed that genuine advances in human knowledge depend instead upon the proper exercise of good judgment in assenting to opinions suitable to the ideas with which they are concerned. [King, pp. 388-398]
Locke rarely commented explicitly on the relation of his own work with that of other thinkers. Sharing the wide-spread seventeenth-century scorn for sectarian proponents of scholastic philosophy, he warned that reliance upon supposed authoritiesancient or modernmore commonly hinders than helps the pursuit of truth. [Conduct 24] Nevertheless, Locke wrote with an extensive and thorough knowledge of the philosophical tradition.
Though he decried the evils of the slavish "Aristoteleans," Locke himself often relied upon the writings of Aristotle, especially in matters of logic and ethics. The influence of classical Stoicism, especially as represented by Cicero, is also evident at many points in the Essay. Medieval philosophers and theologians seem to have made rather less of an impression on him, though it is likely he would have known the work of Augustine, Aquinas, and Ockham. Locke expressed great respect for Francis Bacon, on whose discussions of language and logic he relied, but often criticized Thomas Hobbes, whose analyses of volition and political organization clearly influenced his own thinking.
Locke's relationship to the French Cartesians is more complex. Although he obviously respected the fresh initiatives René Descartes had brought to seventeenth-century philosophy, Locke had serious reservations about the success of the Cartesian approach. He explicitly criticized its identification of body with space under the attribute of extension and its emphasis on the ontological argument for God's existence. Although he sometimes presupposed a dualistic account of human nature, Locke disputed many of its Cartesian corrolaries, including the continual thinking of the soul and the absence of thought in animals, and he notoriously suggested the possibility that matter might have the power to think. In general, Locke disavowed the over-reliance on mathematical reasoning at the expense of sensory observation in the pursuit of human knowledge. His letters include several critical examinations of Gassendi and Malebranche as well.
Among his contemporaries, Locke more clearly admired scientists than philosophers. Although he knew many of the Cambridge Platonists, Locke shared few of their convictions, and his attack on innatism may well have been addressed against them. From his friend Robert Boyle he gleaned the distinction between primary and secondary qualities, along with a profound appreciation for the corpuscularian theory of matter. Of course he reserved high praise for the achievements of Isaac Newton, though Locke's grasp of Newtonian mathematics often seems rather shaky, and the letters the two exchanged were most frequently concerned with biblical interpretation. Locke's own training in the medical sciences did occasionally provide ready examples for points under discussion in the Essay.
Despite the modesty with which he offered his epistemological reflections, Locke showed great interest in the public reception they received. Publication of the "Abstract" drew ample attention even before the book itself had appeared, and from that time on, Locke's correspondence was full of suggestions and complaints from other thinkers. Even when he later modified his views, however, Locke rarely acknowledged this reflected the influence of such criticism, which he tended to regard as unjustified attacks borne of malicious mis-reading. He persistently declined to engage in a direct correspondence with
Leibniz; only the hapless Bishop Stillingfleet succeeded in drawing him into a public debate. On the whole, there is little evidence of the openness to critical reflection Locke frequently expressed in his letters to friends like Molyneux, le Clerc, Tyrrell, and Burnett.