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In English, the term soul can refer to a metaphysical entity or to the state of one's character. A philosopher may disdain the first and applaud the second. This entry focuses on the soul as an entity but concludes with noting why work on the soul is often centered on values.

Evolution of the idea

In ancient Greek philosophy the soul was thought of as a principle of life; the soul is what gives a person life as a human being. For Aristotle (384–322 B.C.E.) the soul (Greek, psyche) was identified as the form of the body. Aristotle delimited a host of different kinds of souls befitting nonhuman animal and plant life. In plants, for example, the soul was thought to be comprised of the plant's nutritive and reproductive powers. The human soul shares many of the powers of other living things but has distinctive intellectual powers as well. Aristotle's teacher, Plato (428–348 B.C.E.) thought of the human soul as an immaterial concrete subject capable of preexisting the body and living on after the body's destruction. In the important work De Anima (On the soul), Aristotle hints at an incorporeal, immaterial aspect to the human soul, but falls short of Plato's more enthusiastic delineation of the soul as independent of the body.

The medieval period favored Plato over Aristotle on the soul, until the Italian philosopher and theologian Thomas Aquinas (1225–1274) appropriated and rethought Aristotle's philosophy of nature in a Christian context. While Aquinas more firmly identified the embodiment of the soul in concrete, material terms, he retained belief in an individual's afterlife and did not embrace a thorough materialism.

The early modern era was profoundly ambivalent about the soul. Modern science was deeply suspicious of Aristotle, and the success of mechanical explanations of the material world were not especially hospitable to the soul and its principles of life. The French philosopher and mathematician René Descartes (1596–1650) demarcated the mind as distinct from the body, but increasingly a form of materialism or naturalism gained ground. Unease about the soul as a distinguishable entity was also fueled by some theologians during the Reformation. Some reformers did not believe the Hebrew Bible welcomed Platonism. In the creation story God makes human beings out of the dust of the ground, into which God breathes the breath of life (Gen. 2:7).

Challenges

The wholesale identification of the soul and the body met with obstacles, however. From the vantage point of modern science, matter (and eventually matter and energy) is not intentional; fundamental physical causal processes do not involve beliefs and desires. If complete and adequate explanations of the cosmos do not involve beliefs and desires, how is one to account for, let alone describe, everyday human activities? Very basic reasoning (1 + 1 = 2) seems to be based on beliefs and reasons (because I grasp 1 + 1, and I grasp that 2 is 1 + 1, I see that the mathematical relationship is necessary). Mechanistic science seems to write off such psychological accounts of our reasoning. This causes an especially difficult challenge with a mechanistic philosophy, for such a philosophy is customarily introduced as a theory that ought to be accepted based on some plausible beliefs about the evidence. But if the theory is correct, then beliefs play no essential role in explaining states of the world. In other words, mechanical, reductive materialism faces the danger of undermining the common sense understanding of humans as rational agents.

Materialists have developed different replies. The most dramatic, as represented by contemporary cognitive scientists and philosophers Stephen Stich, Paul Churchland, and Patricia Churchland, has been to deny that there are any such things as beliefs and desires. Other materialists have denied that psychological explanations are truly explanations in the same category as a scientific explanations. Some consider these two options desperate, for the first risks self-refutation (Stich believes that there are no beliefs) or refutation from common sense, while the second recommends a radical dualism more severe than Descartes's. The alternative, deemed by many to be more promising, is to develop some kind of nonreductive materialism, a theory that recognizes the beliefs, desires, and other powers that used to be associated with the soul, and yet views these beliefs as either identical to, constituted by, or emergent upon physical processes. As of the early 2000s, there is no universally accepted version of nonreductive materialism. Perhaps largely because of this lack of consensus on a problem-free form of materialism, there are some prominent philosophers who defend a form of dualism in which the soul is a distinctive, nonphysical entity.

Arguments over the metaphysics of the soul and arguments over values are closely related. If the whole scope of powers associated with the soul (beliefs, desires) does not exist or has no role to play in a mature explanation of the cosmos, then the values that appear to permeate and define human lives seem to be in jeopardy. It was his perception of this plight that led Stich to revise his radical skepticism about beliefs and desires. The moral implications of eliminating beliefs also led Paul Churchland to try to secure morality within his reductive science; he took on this project under a book title that explicitly refers to the soul: The Engine of Reason, the Seat of the Soul (1995).

Some contemporary theologians are highly motivated to see the soul in material terms. Your soul is your material body, functioning physically, psychologically, and spiritually. A dualist view of the soul is sometimes described as more Platonic than Christian. The effort to see human embodiment in integrated terms is easily appreciated, but it is difficult to avoid the dualist implications of the Bible and Christian tradition. If the soul can survive the death of the body (perhaps to be reembodied at the Resurrection), then it appears that the soul and body are not identical.

As in the Christian tradition, Jewish and Islamic philosophers have shifted between material accounts of the soul in the spirit of Aristotlean and Platonic mind-body dualism. Hinduism, Buddhism, and other religions that allow for reincarnation (a rebirth of the soul in distinct material embodiments) explicitly teach or implicitly assume a distinction between body and soul.

While Judaism, Christianity, and Islam have traditionally seen the soul as a substantive individual, enduring over time, Hindu and Buddhist literature have cast the individuality of the soul in more conditional terms. In Advaita Hinduism, different human souls are identical with the singular Divine Being. In the Buddhist tradition, the soul is a composite of perception, intelligence, form, feeling, and volition.

Popular culture in North America since the mid-1980s has seen a great revival of talk about the soul. Popularized forms of Renaissance Platonism have become fashionable. There is also some effort by philosophers to rekindle language about the soul in which having a soul is understood to involve depth of character or a meaningful presence or availability. People may be said to have a soul when they have deep convictions and integrity. The result is that there is more than one way to lose one's soul, either through a radical form of materialism, or through ethical failure, or a break down of integrity, or the refusal to lead an examined life.

See also ARISTOTLE; CONSCIOUSNESS STUDIES; DESCARTES, RENÉ; DUALISM; HUMAN NATURE, RELIGIOUS AND PHILOSOPHICAL ASPECTS; IMAGO DEI; MATERIALISM, PLATO; SPIRIT; THOMAS AQUINAS; VALUE

CHARLES TALIAFERRO