After having described how the external world affects humans (i.e., through motion) and gives us sense, memory, and experience, Hobbes now turns his attention to the internal mechanisms that affect human behavior. Hobbes claims that within animals like ourselves there are two types of internal motions: 1) vital motion, which can be thought of as essentially involuntarily bodily functions like our heart pumping, respiration, digestions, etc.; and 2) voluntary motion, like walking, talking, and general movement, which have specific ends in mind.
Humans have no control over their vital motions, which arise due to the body's physical makeup, but our voluntary motions are rooted in thought, and more specifically, thoughts about our appetites and aversions. An appetite drives us towards some desired end, whereas an aversion drives us away from some unwanted end. For example, we may voluntarily hurry across a crosswalk upon the sight of an oncoming car due to our aversion to pain.
According to Hobbes, there are some appetites that are born in us (for example, an appetite for pleasure), and some that we acquire through experience (for example, an appetite for our favorite dish). From our appetites and aversions come the human passions, such as hope, courage, anger, benevolence, and a host of others that Hobbes defines. In addition to basing the passions on our appetites and aversions, Hobbes also defines good an evil with respect to them. Specifically, that which is good "is the object of any mans Appetite," and that which is evil is "the object of his Hate, and Aversion."
Turning from the passions to the intellect of man, Hobbes argues that intelligence or wit can be divided into two types: 1) natural wit, which is not something innate but something we get through experience, and which is mainly exhibited in ordering thoughts towards a particular end; and 2) acquired wit, which we get through instruction and method, and "is grounded on the right use of Speech; and produceth the Sciences." Reason, then, is a type of acquired wit - in fact, it is the type of acquired wit. Differences in human intellects comes from differences in passion (mainly the desire for power), and differences in education. In other words, some men have an appetite for knowledge, while others do not.
This fundamental passion, namely, power, is defined as man's "present means, to obtain some future Good." Of this there are two kinds: 1) original or natural power, namely, the faculties of the body and mind, like strength, intellect, eloquence, etc; and 2) instrumental power, the means to acquire further power, for example, riches, reputation, esteem, etc. Following from these definitions, if I have a desire for food, I can use my natural power - for example, my brute strength - to rob a man of loaf of bread I want; or I could use my instrumental power - for example, my vast riches - to pay him for this loaf of bread. Power, in other words, is a means to an end. The value or worth of man is how "much would be given for the use of his powers." From this definition of worth, we can see that worth is a subjective quality. A rich man might be useless to another rich man, but is priceless to someone in debt.
What drives all humans to action is our constant and unquenchable desire for power "that ceaseth only in Death." Even when we have furthered our original powers, whether natural or instrumental, we are never satisfied with our present amount of power, "because [man] cannot assure the power and means to live well, which he hath present, without the acquisition of more." Offsetting this fundamental appetite is a fundamental human aversion, namely, a fear of pain and death. Due to our "fear of Death, and Wounds," we are naturally disposed to seek peace through society, since society is the only "way by which a man can secure his life and liberty."
While all men are fundamentally driven by our desire for power and our aversion to pain, the differences in the "manners" or behaviors of men stem from a lack of proper (philosophical) knowledge of how to achieve such peace. This is precisely the project that Hobbes is undertaking. Only by understanding the nature of our desire for power, which Hobbes has carefully argued for beginning with his definition of sense, can we have a proper understanding of how to achieve peace. Hobbes believes that past philosophical treatments of the topics of man and human nature have not employed such a rigorous philosophical treatment, and have instead relied upon custom (that which has always been taught as true) or esteem (that which is taught by those with supposed unique insight into truth) without properly examining the ordering of conditions and relations between cause and effect.
Since we know that acquired wit is the kind used in reasoning and science, it is important to note what precisely Hobbes means and does not mean when he refers to science. Science is, according to Hobbes "conditionall Knowledge, or Knowledge of the consequence of words." Beginning with established definitions is integral to science. When an argument does not begin with definitions, or moves improperly from step-to-step, its end product is but opinion. Again, the type of science Hobbes seeks to establish with his philosophy does not claim absolute truth, as "no discourse whatsoever, can End in absolute knowledge of Fact, past, or to come. For, as the knowledge if Fact, it is originally, Sense; and ever after, Memory. And for the knowledge of Consequence, which I have said before is called Science, it is not Absolute, but Conditionall." Additionally, there are two types of knowledge, one of which has its place in science, the other of which does not. Knowledge of fact comes from sense and memory, and serves as the basis of history. Knowledge of consequence, "the Knowledge required in a Philosopher," is conditional and composed of if-then statements, which serves as the basis of Science.
Fear serves not just as the driving force behind our desire for peace, but is also the foundation of religion. According to Hobbes, the natural cause of religion is anxiety of the future, which is furthered by ignorance of cause and effect relations. Religion comes from three sources: 1) curiosity into the causes of events; 2) curiosity of the causes of these causes; 3) forgetting the order of things and past causes and effects, which is then attributed elsewhere, i.e., to God. In other words, when we see an event and cannot discern the natural cause of it, we attribute this to a supernatural or divine power.
Unfortunately, religion has been misused to make men obedient to a self-serving authority. When a state falls upon famine or economic hardship, religious 'authorities' will claim this is because of divine causes, or because the citizens have not been pious enough. Not knowing the true causes of their conditions (for example, poor agricultural policy or government corruption), citizens will not fault their government for their hardships. Not only does this offend true religion, since it is a perversion of proper religious doctrine, but this is also counter-productive to a society's well-being, as mismanagement and chaos are remain unchecked and run rampant throughout the public.
In these chapters one can see Hobbes' geometry-inspired methodology at work again. Since the external world is constantly in motion, and their motions set off corresponding motions within our bodies that we experience as sensations, we experience constant and insatiable appetites and desires, which put us in perpetual competition with other men for the objects of these desires. If bodies were naturally at rest, then man's appetites would also be finite, and we could peacefully coexist in a state of nature. Thus, Hobbes' premise regarding motion is the cornerstone of this argument, and as we will come to see, of the entirety of his argument concerning man and government.
From these chapters one can see the importance that fear plays in Hobbes' philosophy. Yet precisely what this fear is of is a subject of debate. Generally speaking, it is "at once the principal cause of war and the principle means to peace...[and] the basis both of man's most urgent plight and his only possible escape" (Blits). At its fundamental level, it is not a fear of other men or (as will later be elucidated) of God or spirits. As Blits argues, both of these fears derive from man's basic fear of the unknown. Without experience or knowledge of the external world, and compounded with an ignorance of the causes of events, we have a fear of anything that is unfamiliar to us. That is to say, upon birth we have a fear of everything, and only later do we come to fear particular objects like other men.
In a particularly short chapter (IX) Hobbes lays out in diagrammatic form the manner in which the branches of knowledge are organized. Given Hobbes admiration for the accomplishments and methods of geometry, one might expect to find all knowledge emanating from geometry or general mathematics. Yet in Hobbes' tree of knowledge geometry does not serve as the roots, but is instead one of its branches. In fact, he places geometry as one of the small branches on the side of natural philosophy, (knowledge of fact), and his project of politics/civil philosophy on the side of knowledge of consequences. These two divisions fall under the most general heading of science. What is revealing about this is that Hobbes does not believe philosophy emanates from, or should be grounded in geometry, but rather that the same strict methodology used in geometry should be applied to philosophy.
Contrast this with Descartes' Discourse on Method (1637). For Decartes, who sought to base philosophy on his famous principle, "I think, therefore I am," the tree of knowledge began with metaphysics as its roots, physics as its trunk, and ethics, medicine, and other subjects as its branches. In other words, physics or natural philosophy sprung from metaphysics, in contrast to Hobbes' division of these two fields of knowledge. Kant's Critique of Pure Reason (1781) included another attempt to apply mathematical principles to philosophy. Kant sought to bring philosophy "on equal footing" with mathematics, similar to Hobbes, by applying its rigorous methodology and exact definitions.
One criticism of Hobbes is that his definitions of good and evil are entirely amoral. Indeed, by making good and evil inherently subjective qualities, Hobbes comes to the conclusion that "There being nothing simply absolutely so [good or evil]; nor any common Rule of Good and Evill, to be taken from the nature of the objects themselves." Whether this implies a form of moral relativism is besides the question. Hobbes is not concerned with how men ought to act according to some objective morality, but instead grounds obligation on man's inherent desire for self-preservation. Pragmatically speaking, this makes for a much more efficacious normative philosophy. Hobbes does not explore normativity further than simply saying, "If you want to preserve your life, you ought to do X." Indeed, he explicitly denies the existence of some universal moral truth ("any common Rule of Good of Evill"), so any arguments progressing from such a principle with be invalid.