David Hume, A Treatise of Human Nature (1739)

Even for those of us who are not professional scholars, there is value in reading the original words of someone like David Hume rather than reading only what others have said about him. Part of that value is found simply in the exercise of mentally transporting yourself back in time to better understand the 18th century period in which he lived and how new ideas were being debated at that time. Another part of that value will be retrieved the next time I read about David Hume, and a greater appreciation of the point the author is making. Among Enlightenment philosophers, I chose Hume because he is too frequently cited in the books I read to not pay attention to him.

Hume, I have surmised, is regrettably overlooked by Americans in their surveys of philosophy. Other Enlightenment philosophers --- notably John Locke --- garner more attention because they were sources of inspiration for the development of American political and legal traditions. Locke is associated with the idea of "natural rights" and declared truths "we hold to be self-evident." In the field of epistemology, Locke probably receives more attention than Hume in surveys of philosophy because he was an earlier proponent of empiricism, which emphasizes the role of experience and the senses in our understanding of objects in the world over the view that knowledge is innate. Within the community of contemporary philosophers of the mind as well as psychologists and neuroscientists, Hume has received his credit for his contribution to our understanding of how the mind works --- even more so than Locke --- and that would suggest that survey courses in philosophy might reorient their Enlightenment-era discussions of knowledge and the mind to pay more attention to Hume to better appreciate how our understanding of the mind has evolved since the 18th century.

A Treatise of Human Nature is an 18th century version of How The Mind Works. It advances the concept of associationism, a concept which dominated psychology in the 19th and early 20th centuries, in greater detail than anyone had previously discussed. What Hume did not have at his disposal in the 1730s was a body of empirical research from the fields of psychology, biology, and neuroscience to inform his inquiry into human nature. He had the works of philosophers who preceded him, which he had digested prior to embarking on his Treatise, and his own series of what he called "experiments" --- introspective thinking about how his own mind and body worked and thinking about others to assess whether he could generalize from his own experience. For this reason, the Treatise carries the subtitle "Being an Attempt to Introduce the Experimental Method of Reasoning Into Moral Subjects."

Hume is an example of John Searle's Enlightenment-era philosopher trying "to cope with the problem of skepticism." (See previous January 21, 2011 post). "As to those impressions," Hume writes, "which arise from the senses, their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and 'twill always be impossible to decide with certainty, whether they arise immediately from the object or a produced by the creative power of the mind, or are derived from the author of our being." In other words, the representations of things in our mind come from our sense experiences and we can never know with certainty that the object of our mind's attention produces that impression or whether it is a priori in our minds because of the act of a deity ("the author of our being."). The Treatise represents Hume's effort to "cope" with this inability to know anything directly with certainty, and he determines that the mind's ability to associate ideas enables it to make inferences that form the basis of our knowledge about external objects to which our senses are exposed. The three principle qualities that enable the mind to associate or connect various ideas are resemblance, contiguity (in time and space), and cause and effect.

In his book Mind, John Searle writes that "most philosophers will agree [that Hume's account of causation] is one of the most impressive pieces of philosophical prose ever written in the English language." Why does he say this? Because Hume reasoned a way in which we can generalize about reality from specific sense experiences. Hume describes a principle of causation and a principle of causality, which are not the same. The first says every effect has a cause; the second says that like effects have like causes. We experience something through sensation, but the only quality from that single experience is one of contiguity (before and after, or next to), but we do not necessarily make a connection between that that single experience and what caused it without a constant repetition of similar experiences (resemblances). The greater the regularity of those similar experiences produces a "felt determination of the mind" on which a generality is based. Hume notes that probability plays a role here in creating Belief. "Should it be demanded why men form general rules, and allow them to influence their judgment, even contrary to present observation and experience, I should reply, that in my opinion it proceeds from those very principles, on which all judgments concerning causes and effects depend. Our judgments concerning cause and effect are derived from habit and experience; and when we have been accustomed to see one object united to another, our imagination passes from the first to the second, by a natural transition, which precedes reflection [that is before we even seriously think about what we just experienced] and which cannot be prevented by it." It is what Searle calls "Hume's regularity theory of causation" that has been influential in the philosophy of the mind.

One can be critical of Hume, because he does not believe that we actually experience necessary connections between things (causation), or that we actually experience our conscious selves and are forced to rely on frequently repeating, resembling events that strengthen the force of our perceptions before we can form "beliefs" about external objects or our identity, without having to disparage his analysis of how the mind works. Hume's account of human nature integrates sensation, feelings, emotions, and memory --- what today we recognize as the neurobiological network of the human body, including the brain, that constitutes a conscious human agent. "Belief," says Hume, "is more properly an act of the sensitive, than the cogitative part of our natures."

This book is intended to be a treatise on the nature of humans, but Hume consciously ducks discussing human biology: "The examination of our sensations belongs more to the anatomists and natural philosophers [scientists] than to moral; and therefore shall not at present be entered upon." And even if he had not avoided the biology of what makes us human, today's reader would have learned little in light of the fact that Hume did not enjoy what John Searle notes that we enjoy in the 21st century: "a huge accumulation of knowledge [about biological systems, biological evolution, DNA and reproduction, embryology, etc.], which is certain, objective, and universal." (See previous post of January 21, 2011). But the absence of that knowledge from Hume's treatise should not cause one not to marvel at the depth of his introspection on human nature.

It is important to give Hume credit for recognizing the role of feelings and, what he calls "passions" in human nature and human decision-making. Sensations (experience) give rise to passions (reflective impressions). Sensations are either pleasurable (good) or painful (evil,bad), with varying degrees of each known to us. Certain passions are associated with pleasure (e.g., pride, love, benevolence, compassion, hope, joy), other passions are associated with pain (e.g., humility, hate, anger, malice, envy, fear, grief). The different passions vary by degree, which Hume labels "violent" or "calm." Like knowledge, passions are stronger or weaker because of repetition in our experience and the extent to which those experience become embraced by custom [culture]. Reason, says Hume, is not some objective, fully-informed distinct mental state separate from the passions; it is nothing more than a popular term for the "calm" passions, reflecting Hume's view that reason is never isolated from our emotions that are derived from our experience (sensations). Understood in this light, Hume foreshadows the tradition of Williams James that continues today in the works of Antonio Damasio (The Feeling of What Happens), which recognizes that emotions and feelings are caused by physiological changes attributable to electro-chemical stimuli in the neurobiological system.

The modern reader of the philosophy of mind, psychology, biology, and neuroscience will recognize that Hume identified and seized on human attributes and behavior that are now more completely understood in biological terms. For example, Hume's statement that "The mind is a kind of theatre, where several perceptions successively make their appearance; pass, re-pass, glide away, and mingle in an infinite variety of postures and situations" reminds one of Damasio's reference to consciousness as a 'movie within a movie.' The difference between Hume and contemporaries such as Damasio is revealed in Hume's statement: "The comparison to the theatre must not mislead us. They are the successive perceptions only, that constitute the mind; nor have we the most distant notion of the place, where these scenes are represented, or of the materials, of which it is composed." For Damasio and his peers, while we may not have a full account of the mind and brain, we no longer have a "distant notion" of the place where and how images are represented in the brain and we have a very good of the physical attributes of which the brain is composed.

Hume even foreshadows our modern discussion of mirror neurons when he writes that "the minds of men are mirrors to one another, not only because they reflect each other's emotions, but also because those rays of passions, sentiments and opinions may be often reverberated, and may decay away by insensible degrees," and he connects this observation to human empathy and sympathy for fellow humans. Later, in Book 3, Hume writes, "When I see the effects of passion in the voice and gesture of any person, my mind immediately passes from these effects to their causes, and forms such a lively idea of the passion, as is presently converted into the passion itself. In like manner, when I perceive the causes of any emotion, my mind is conveyed to the effects, and it is actuated with a like emotion." In statements like this one senses a primitive Enlightenment precursor to the research of Marco Iacoboni and others as described in Mirroring People: The Science of Empathy and How We Connect. (See September 18, 2009 post).

The Treatise does not end with Hume's conclusion about the nature of the human mind and how sensory perceptions connect to feelings and emotions that become experiences, memories, and ultimately beliefs about the external world and free-will, but the Treatise expands to include the construction of a cultural reality and social institutions for the regulation of human behavior (customs, rules, and law). Hume is not a social contractarian in the tradition of Hobbes, Rousseau (and later, Rawls). Morality and social structure do not evolve from human reason: "morality is more properly felt than judged," indicating that justice is derived from our impressions, not from reason. The passion sympathy [empathy] is the chief source of our moral distinctions, says Hume. Consistent with Hume's "system" of the human understanding that is described in Book 1, our sensory experiences of pleasure and pain give rise to positive and negative passions, which in turns leads to a propensity toward something that is favored (in the case of positive passions) or an aversion from something that is disfavored (in the case of negative passions). In either case, we are talking about self-interest and self-interest includes a recognition that reciprocal relations with other humans (including promise-making behavior) leads to a moral sense of virtue (favored) and vice (disfavored). After awhile, humans develop a general "sense" of common interest. This leads to the development of social rules, laws, and institutions to enforce them. This process is not the outcome of a rational bargain and a signed contract, but it is a process that reflects an evolving tendency toward stasis, much as the human body pits the positive and negative passions that tend toward homeostasis.

We can also recognize in the Treatise a primitive discussion of whether altruistic acts are confined to biological relations (kin) or are capable of being expanded to wider societal relations and nations. Hume writes, "When experience has once given us a competent knowledge of human affairs and has taught us the proportion they bear to human passion, we perceive that the generosity of men is very limited, and that it seldom extends beyond their friends and family, or, at most, beyond their native country." This same sentiment is debated today in Holldobler and Wilson's The Superorganism (see November 4, 2009), Oren Harman's The Price of Altruism (see October 13, 2010 post), and Frans DeWaal's The Age of Empathy (see November 9, 2010 post).

Hume clearly disputes Bernard Mandeville's view that man is driven by egotistical impulses, seeking self-preservation and advancement. (See January 30, 2010 post). Hume does not deny egotistical impulses and the pursuit of self-preservation, but for every passion that Hume identifies there is a counter-passion: in the case of self-interest, there is sympathy and empathy for others. In Mandeville's view, it is societal institutions that regulate and restrain man's self-seeking drives; in Hume's vision, sympathy, empathy, generosity, and reciprocal behavior are part of human nature. Hume's assessment of human nature has clearly prevailed from the modern view of biology, psychology, and neuroscience. In this regard, Hume is closer to his fellow Scotsman, Adam Smith, whose Theory of Moral Sentiments is at the core of Amartya Sen's The Idea of Justice (see January 11, 2011 post).

Nearly four centuries after Hume wrote his Treatise, we recognize that his observations on human nature are not all that far from those which science and experiment confirm for us today. Associationism may no longer hold sway in our view of how the mind works, but the linkage between sensations, feelings, emotions, reflection, and reasoning, which Hume describes in the Treatise, is the same linkage that neuroscientists describe today. The limitation of the treatise, which I think we will appreciate from the next book off The Bookshelf by Antonio Damasio, is that Hume did not fully appreciate how we construct a personal identity for ourselves. Hume says, "The identity, which we ascribe to the mind of man, is only a fictitious one, and of a like with that which we ascribe to vegetables and animal bodies. It cannot, therefore, have a different origin, but must proceed from a like operation of the imagination upon like objects." In other words, Hume says that we come to know our self in the same way we come to know external objects. Presumably this means Hume is coping with his skepticism over his own identity just as much he is coping with his skepticism toward the broccoli he ate for dinner. Let's see what Damasio has to say.