In his book On the Soul, Aristotle gave the following definition of soul: “The soul is the first actuality of a natural body that is potentially alive” (412a27). This first actuality of the body is the immaterial form of the body. This form is not the shape of something but rather a set of functions that make a thing what it is. This conception of soul as form influenced St. Thomas Aquinas in the medieval period and influenced Leibniz in the modern period. But our contemporary world may have found a new home for it due to the creation of computers and the introduction of the software/hardware distinction. The modern appropriation makes some significant changes and by no means preserves all of Aristotle’s and/or Aquinas’ full meaning. But one similarity is still there and can be summarized as follows: soul as form is like the software that organizes the hardware of the body. The soul, like software, includes functions that could be implemented in a variety of hardware systems. For some, this vision of the soul opens up the possibility that we can survive the death of our bodies or our hardware. The essential thing for cheating death is not the preservation of the hardware system but the preservation of the abstract patterns of functions and data. For example, leading cosmologists John Barrow and Frank Tipler identify the Aristotelian soul with a computer program:
“An intelligent being—or more generally, any living creature—is fundamentally a type of computer . . . the really important part of a computer is not the particular hardware, but the program; we may even say that a human being is a program designed to run on particular hardware called a human body, coding its data in very special types of data storage devices called DNA molecules and nerve cells. The essence of a human being is not the body but the program which controls the body; we might even identify the program which controls the body with the religious notion of a soul, for both are defined to be non-material entities which are the essence of a human personality. In fact, defining the soul to be a type of program has much in common with Aristotle and Aquinas’ definition of the soul as ‘the form of activity of the body’. A living human being is a representation of a definite program rather than the program itself. In principle, the program corresponding to a human being could be stored in many different forms.”
In his book The Physics of Immortality, Tipler reiterates some of the above but also expands on the notion of an abstract program:
“There is actually an astonishing similarity between the mind-as-computer-program idea and the medieval Christian idea of the “soul.” Both are fundamentally “immaterial”: a program is a sequence of integers, and an integer—2, say—exists “abstractly” as the class of all couples. The symbol “2” written here is a representation of the number 2, and not the number 2 itself. In fact, Aquinas (following Aristotle) defined the soul to be “the form of the activity of the body.” In Aristotelian language, the formal cause of an action is the abstract cause, as opposed to the material and efficient causes. For a computer, the program is the formal cause, while the material cause is the properties of the matter out of which the computer is made, and the efficient cause is the opening and closing of electrical circuits. For Aquinas, a human soul needed a body to think and feel, just as a computer program needs a physical computer to run.”
Philosopher Daniel C. Dennett also believes the mind is akin to software. Dennett argues that the self is a fictional character told by one’s brain that is constantly writing and re-writing one’s autobiography. This specifically human activity of presenting ourselves to others and having others present themselves to us generates narratives: and the self is nothing other than an abstract “center of narrative gravity” which, although fictional, plays an important role in organizing our lives. He links his vision of the self to immortality:
“Now if you were a soul, a pearl of immaterial substance, we could “explain” your potential immortality only by postulating it as an inexplicable property, an ineliminable virtus dormitiva of soul-stuff. And if you were a pearl of material substance, some spectacularly special group of atoms in your brain, your morality would depend on the physical forces holding them together (we might ask physicists what the “half-life” of a self is). If you think of yourself as the center of narrative gravity, on the other hand, your existence depends on the persistence of that narrative (rather like the Thousand and One Arabian Nights, but all a single tale), which could theoretically survive indefinitely many switches of medium, be teleported as readily (in principle) as the evening news, and stored indefinitely as sheer information. If what you are is that organization of information that has structured your body’s control system (or, to put it in its more usual provocative form, if what you are is the program that runs on your brain’s computer), then you could in principle survive the death of your body intact as a program can survive the destruction of the computer on which it was first created and first run.” Dennett concludes that “The idea that the Self—or the soul—is really just an abstraction strikes many people as simply a negative idea, a denial rather than anything positive. But in fact it has a lot going for it, including—if it matters to you—a somewhat more robustly conceived version of potential immortality than anything to be found in traditional ideas of the soul…”
 Barrow and Tipler, The Anthropic Cosmological Principle (New York: Oxford University Press, 1986), p. 659.
 Frank Tipler, The Physics of Immortality (New York: Doubleday, 1994), p. 127.
 Dennett, Consciousness Explained (New York: Little, Brown, and Co., 1991), p. 430.
 Ibid., 368.