Hume observes that while we may perceive two events that seem to occur in conjunction, there is no way for us to know the nature of their connection. Based on this observation, Hume argues against the very concept of causation, or cause and effect. We often assume that one thing causes another, but it is just as possible that one thing does not cause the other. Hume claims that causation is a habit of association, a belief that is unfounded and meaningless. Still, he notes that when we repeatedly observe one event following another, our assumption that we are witnessing cause and effect seems logical to us. Hume holds that we have an instinctive belief in causality, rooted in our own biological habits, and that we can neither prove nor discount this belief. However, if we accept our limitations, we can still function without abandoning our assumptions about cause and effect. Religion suggests that the world operates on cause and effect and that there must therefore be a First Cause, namely God. In Hume’s worldview, causation is assumed but ultimately unknowable. We do not know there is a First Cause, or a place for God.
Induction is the practice of drawing general conclusions based on particular experiences. Although this method is essential to empiricism and the scientific method, there is always something inherently uncertain about it, because we may acquire new data that are different and that disprove our previous conclusions. Essentially, the principle of induction teaches us that we can predict the future based on what has happened in the past, which we cannot. Hume argues that in the absence of real knowledge of the nature of the connection between events, we cannot adequately justify inductive assumptions. Hume suggests two possible justifications and rejects them both. The first justification is functional: It is only logical that the future must resemble the past. Hume pointed out that we can just as easily imagine a world of chaos, so logic cannot guarantee our inductions. The second justification is that we can assume that something will continue to happen because it has always happened before. To Hume, this kind of reasoning is circular and lacks a foundation in reason. Despite the efforts of John Stuart Mill and others, some might argue that the problem of induction has never been adequately resolved. Hume left the discussion with the opinion that we have an instinctual belief in induction, rooted in our own biological habits, that we cannot shake and yet cannot prove. Hume allows that we can still use induction, like causation, to function on a daily basis as long as we recognize the limitations of our knowledge.
Hume proposes the idea that moral principles are rooted in their utility, or usefulness, rather than in God’s will. His version of this theory is unique. Unlike his Utilitarian successors, such as John Stuart Mill, Hume did not think that moral truths could be arrived at scientifically, as if we could add together units of utility and compare the relative utility of various actions. Instead, Hume was a moral sentimentalist who believed that moral principles cannot be intellectually justified as scientific solutions to social problems. Hume argues that some principles simply appeal to us and others do not. Moral principles appeal to us because they promote our interests and those of our fellow human beings, with whom we naturally sympathize. In other words, humans are biologically inclined to approve and support whatever helps society, since we all live in a community and stand to benefit. Hume used this simple but controversial insight to explain how we evaluate a wide array of phenomena, from social institutions and government policies to character traits and individual behavior.
Hume denies that reason plays a determining role in motivating or discouraging behavior. Instead, he believes that the determining factor in human behavior is passion. As proof, he asks us to evaluate human actions according to the criterion of “instrumentalism”—that is, whether an action serves the agent’s purpose. Generally, we see that they do not and that human beings tend to act out of some other motivation than their best interest. Based on these arguments, Hume concludes that reason alone cannot motivate anyone to act. Rather, reason helps us arrive at judgments, but our own desires motivate us to act on or ignore those judgments. Therefore, reason does not form the basis of morality—it plays the role of an advisor rather than that of a decision-maker. Likewise, immorality is immoral not because it violates reason but because it is displeasing to us. This argument angered English clergy and other religious philosophers who believed that God gave humans reason to use as a tool to discover and understand moral principles. By removing reason from its throne, Hume denied God’s role as the source of morality.
Hume argues that an orderly universe does not necessarily prove the existence of God. Those who hold the opposing view claim that God is the creator of the universe and the source of the order and purpose we observe in it, which resemble the order and purpose we ourselves create. Therefore, God, as creator of the universe, must possess intelligence similar, though superior, to ours. Hume explains that for this argument to hold up, it must be true that order and purpose appear only as a direct result of design. He points out that we can observe order in many mindless processes, such as generation and vegetation. Hume further argues that even if we accept that the universe has a design, we cannot know anything about the designer. God could be morally ambiguous, unintelligent, or even mortal. The design argument does not prove the existence of God in the way we conceive him: all-knowing, all-powerful, and entirely beneficent. The existence of evil, Hume holds, proves that if God exists, God cannot fit these criteria. The presence of evil suggests God is either all-powerful but not completely good or he is well-meaning but unable to destroy evil, and so not all-powerful.
Hume asks us to consider what impression gives us our concept of self. We tend to think of ourselves as selves—stable entities that exist over time. But no matter how closely we examine our own experiences, we never observe anything beyond a series of transient feelings, sensations, and impressions. We cannot observe ourselves, or what we are, in a unified way. There is no impression of the “self” that ties our particular impressions together. In other words, we can never be directly aware of ourselves, only of what we are experiencing at any given moment. Although the relations between our ideas, feelings, and so on, may be traced through time by memory, there is no real evidence of any core that connects them. This argument also applies to the concept of the soul. Hume suggests that the self is just a bundle of perceptions, like links in a chain. To look for a unifying self beyond those perceptions is like looking for a chain apart from the links that constitute it. Hume argues that our concept of the self is a result of our natural habit of attributing unified existence to any collection of associated parts. This belief is natural, but there is no logical support for it.