Naturalism asserts that the world is of a piece; everything we are and do is included in the space-time continuum whose most basic elements are those described by physics. We are the evolved products of natural selection, which operates without intention, foresight or purpose. Nothing about us escapes being included in the physical universe, or escapes being shaped by the various processes – physical, biological, psychological, and social – that science describes. On a scientific understanding of ourselves, there’s no evidence for immaterial souls, spirits, mental essences, or disembodied selves which stand apart from the physical world.
What constitutes knowledge
Naturalism as a worldview is based on the premise that knowledge about what exists and about how things work is best achieved through the sciences, not personal revelation or religious tradition. The knowledge we have of ourselves and our place in nature is the achievement of a collective effort to construct a consistent view of the world that permits prediction and control. This effort proceeds by experiment and rational inquiry, and the knowledge gained is always subject to further testing as understanding matures. Wanting something to be true, or having the intense personal conviction that something is true, are never grounds for supposing that it is true. Scientific empiricism has the necessary consequence of unifying our knowledge of the world, of placing all objects of understanding within an overarching causal context. Under naturalism, there is a single, natural world in which phenomena arise.
The causal view
From a naturalistic perspective, there are no causally privileged agents, nothing that causes without being caused in turn. Human beings act the way they do because of the various influences that shape them, whether these be biological or social, genetic or environmental. We do not have the capacity to act outside the causal connections that link us in every respect to the rest of the world. This means we do not have what many people think of as free will, being able to cause our behavior without our being fully caused in turn.
As strictly physical beings, we don’t exist as immaterial selves, either mental or spiritual, that control behavior. Thought, desires, intentions, feelings, and actions all arise on their own without the benefit of a supervisory self, and they are all the products of a physical system, the brain and the body. The self is constituted by more or less consistent sets of personal characteristics, beliefs, and actions; it doesn’t exist apart from those complex physical processes that make up the individual. It may strongly seem as if there is a self sitting behind experience, witnessing it, and behind behavior, controlling it, but this impression is strongly disconfirmed by a scientific understanding of human behavior.
Responsibility and morality
From a naturalistic perspective, behavior arises out of the interaction between individuals and their environment, not from a freely willing self that produces behavior independently of causal connections (see above). Therefore individuals don’t bear ultimate originative responsibility for their actions, in the sense of being their first cause. Given the circumstances both inside and outside the body, they couldn’t have done other than what they did. Nevertheless, we must still hold individuals responsible, in the sense of applying rewards and sanctions, so that their behavior stays more or less within the range of what we deem acceptable. This is, partially, how people learn to act ethically. Naturalism doesn’t undermine the need or possibility of responsibility and morality, but it places them within the world as understood by science. However, naturalism does call into question the basis for retributive attitudes, namely the idea that individuals could have done otherwise in the situation in which their behavior arose and so deeply deserve punishment.
The source of value
Because naturalism doubts the existence of ultimate purposes either inherent in nature or imposed by a creator, values derive from human needs and desires, not supernatural absolutes. Basic human values are widely shared by virtue of being rooted in our common evolved nature. We need not appeal to a supernatural standard of ethical conduct to know that in general it’s wrong to lie, cheat, steal, rape, murder, torture, or otherwise treat people in ways we’d rather not be treated. Our naturally endowed empathetic concern for others and our hard-wired penchant for cooperation and reciprocity get us what we most want as social creatures: to flourish as individuals within a community. Naturalism may show the ultimate contingency of some values, in that human nature might have evolved differently and human societies and political arrangements might have turned out otherwise. But, given who and what we are as natural creatures, we necessarily find ourselves with shared basic values which serve as the criteria for assessing moral dilemmas, even if these assessments are sometimes fiercely contested and in some cases never quite resolved.