Steven Baldner; The Soul in the Explanation of Life


 Steven Baldner

Consider the following quotation, taken from a contemporary textbook in biology.  The quotation explains the first of the fundamental principles for modern biology.

                One of the basic tenets of modern biology is that all of the phenomena of life are governed by, and can be explained in terms of, chemical and physical principles.  Until early in the present century most people, biologists and laymen alike, held that life processes differed in some fundamental way from those of nonliving systems.  With the vast increase since then in our understanding of chemical and physical principles it has become clear that the myriad phenomena of life, although much more complex than nonliving systems, can be explained in chemical and physical terms without postulating some mysterious vital force.  The properties of living cells and organisms that at one time seemed so mysterious, now appear to be quite straight forward.  Many of the complex phenomena of living systems can be reproduced in the test tube under appropriate conditions.  The corollary of this belief is, of course, that if we knew enough about the chemistry and physics of living systems we could re-create life in the test tube.[1]

The authors of this passage make a strict disjunction between two types of explanation:  explanation in chemical and physical terms and explanation in terms of “some mysterious vital force”. Either we regard living beings scientifically as chemical, molecular, and atomic--and as nothing more than these--or we give up science altogether and talk about the unknowable as the cause of the knowable.  This strict disjunction is one that seems to dog philosophy and the philosophy of nature:  either materialism or idealism; either mechanism or vitalism; either scientism or the occult.  We are always forced, it seems, to make a hard choice, for tertium non datur.  Since the authors of this passage are scientists, they choose the empirical, the material, or the scientifically knowable, but the implication of their choice is that to choose anything more than the strictly material (that is, more than the atomic, molecular, or chemical) is to choose what is anti-scientific.

                I argue that there is a third possibility, that it makes very good sense to say that the living is something more than its chemical constituents.  This “something more” is its substantial form, the very principle and ultimate cause of its being alive.  But this principle of substantial form, traditionally called the soul, need not be understood in some way that is anti-scientific.  With Aristotle and St. Thomas Aquinas, I think that I can make my case.

                The position advanced by these authors is called reductionism:  the position that more complex kinds of reality are nothing but aggregates of simpler kinds of reality.  The reductionist wishes to say that the whole is not more than the sum of its parts.  In biology, the reductionist's argument would be something like this.  The biologist explains life in terms of what is scientifically knowable, and what is scientifically knowable is empirically verifiable.  Nothing other than the chemical make-up of a living organism is empirically verifiable.  Hence, the living organism is nothing more than its chemical make-up.

                Now the biologist will not claim that only the immediately observable is real, for he will allow that it is possible to infer the existence of realities that cannot be observed from realities that can.  The biologist knows about the existence of proteins, for example, in a cell by introducing radioactively labelled antibodies specific to the protein he wishes to identify.  From resultant traces of radioactivity he infers the existence of proteins that he cannot directly observe.  Once scientists have some evidence for the existence of a non‑ observable reality, they attempt to find other evidence to confirm the existence of what is not observable.  The evidence must ultimately be empirical, so that it may be said that all of what is known in science has an empirical basis.

                When the experimental biologist investigates living beings, he often proceeds analytically.  That is, he separates and isolates, often, as in dissection, by violent means, the constituent parts of an organism.  These parts may be organs or they may be chemical substances, but in either case the biologist is dealing with something that is, either actually or potentially, a substance in itself.  An organ is a substance in the sense that it is a part of a substance, and a chemical within an organism is a substance in the sense that, although it does not exist as a substance in the organism, it is virtually or potentially present in the substance so that it can be extracted and when extracted made to exist actually as a substance.  The substantial form, however, is not like a substantial part.  The substantial form cannot be extracted from the whole or isolated analytically to be examined separately.  It is the cause of the whole as a whole, and it is therefore not visible to the experimenter's methods which are analytical.  The experimenter works by splitting an organism apart to see what its constituent parts and elements are; the result of such splitting never reveals some part or element called substantial form or soul.  Hence, it seems that the form is irrelevant to the work of the experimental biologist.

                In one sense it is true that the substantial form or soul is irrelevant to the work of the experimental biologist.  As one attempting to explain the constituents of life, he is not concerned with the question, simply, of what life is.  But by focusing on the constituents of life, he is not thereby entitled to give a full answer to the question, which is properly philosophical, of what life is.  He can explain what is materially required for life--he can provide the material and some of the efficient causes of life--but he cannot say what life is without appealing to the substantial form.  For the practice of the biologist, then, a reductionism is justified, provided that the reduction is understood to be only for the purposes of a certain restricted discipline.  The reduction, however, must not be understood to preclude the wider, philosophical question of what life is.  To give an answer to that question, as I shall argue, we must appeal to the substantial form of life, known traditionally as the soul.

                The most important source for Aristotle's thinking on life is the De anima, and we shall focus especially on the first two chapters of book II, where Aristotle gives his two definitions of the soul.  The very first point that Aristotle makes is that the reality of life belongs to substances.[2]  We must, therefore, recognize the distinction between substance and accident, and recognize that the soul, which is the principle of life, is not an accident of living things.  That is, it does not inhere in something else as in a subject.

                Substance, Aristotle points out, can be taken in three senses:  as matter, as form, and as the composite of matter and form.  Aristotle sets his discussion of life in the context of his hylomorphic philosophy, developed primarily in the Physics.  All natural substances are composites of form and matter, form as the principle of actuality and matter as the principle of potentiality, the composite being what is the existent thing.  Aristotle's hylomorphism is not, I would argue, a mere theory, in the sense that it would be merely a dialectical attempt to explain phenomena not fully understood.  Rather, I would contend that the hylomorphism is necessarily required in order to explain the fundamental reality of motion in all living things.  I am not going to give the argument here, but the only way to deny the hylomorphic composition of natural things is to deny the reality of motion.  The point I want to make is the vast importance of the doctrine for what Aristotle is trying to do in the De anima.  Aristotle wishes to explain life.  He has already argued for the explanatory value of form and matter.  It is prima facie obvious to him that the explanation of life will be an explanation of the actuality, or form, of life.  The question for him is, what is this form?

                To put the question another way, if we already recognize, as Aristotle does, the forms of natural constituents, such as elements, why is there a need for some form that goes beyond these constituents?  An atom, for example, could be said to be a substance[3] and the sub-atomic particles could be said to be its matter.  The atom, or more likely the molecule, is a new reality with new properties above and beyond the properties of the constituent particles.  This new reality or actuality has inherent, spontaneous activity and thus must have something that is appropriate to itself as a whole--it must be a new form, in Aristotle's terms.  Similarly, the particles are subject to change and could be transformed into other particles.  The given form of any particle is often described, today, in terms of mass, and the potentiality for other forms is said to be energy.  Mass and energy are, thus, modern analogues to Aristotle's act and potency.  One could say, therefore, that there is a kind of acceptance of form and matter at the basic physical or chemical level insofar as there is an acceptance of the fundamental convertibility of mass and energy.  Furthermore, many would accept that at the atomic level and again at the molecular level there are new realities, not found in the elemental constituents.  But must we recognize yet another level of reality, another kind of form, to correspond to the level of life?  My point at is simplest is that, if we accept the reality of non-living substances, what evidence is there that living substances are anything more than mere aggregates or arrangements of non-living substances.  What argument does Aristotle give to show that living things cannot be reduced to non-living things?

                Aristotle gives three ways in which the form of a living thing must be radically different from the form of non-living things.  First, a living thing may be alive but not be actually performing all of the activities of being alive.  Actuality, Aristotle points out, is of two sorts.[4]  There is the actuality of possessing an ability to operate, and there is the actuality of performing the operation.  The geometer who is sleeping possesses the actuality of geometry in the first sense, but when he is actually solving geometrical problems he possess the actuality of geometry in the second sense.  The actuality of life (the soul), says Aristotle, is an actuality in the first not in the second sense.  That is to say, as Thomas will later point out,[5] that the powers and operations of the soul are really distinct from the essence of the soul.  The empirical reason for this is that living things do not perform all of the operations of being alive all of the time that they are alive.  Growth, for example, is one of the operations of living beings, but there are times when a living being is alive but not growing.  Sensation and self-motion are operations of at least some living things and they are intermittent operations:  the animal remains alive while not always performing these operations.  In this way the form of a living thing differs sharply from the form of a non-living thing.  There is no distinction in the non-living thing between its possessing its substantial form and its performing its characteristic activities.  As soon as something has mass, for example, it begins to exert gravitational attraction; it does not at times exert such attraction and at other times not.  It does not have the sort of double actuality (a potency for operating and an actual operating) that living things have.

                Second, the form of a living thing must be the form of an organic body.[6]  That is, the body which is able to be alive (has a potency for life) must have distinguishable, spatially separate parts that serve the life the whole.  The heart of a mammal or the roots of a plant have specific functions that serve the whole organism.  From these specific organs we can trace the movement of the blood or the gathering of soil nutrients.  But this is very much unlike the non-living.  The presence or absence of protons might produce an isotope, but the protons are not really spatially distinguishable and the resultant radioactivity, say, is a property of the whole isotope.  It is not an operation of some protons, as the movement of blood is the operation of the heart.  Non-living matter, therefore, does not have distinct organs; it has parts in the sense that any continuous whole can be arbitrarily divided in quantity but it does not have qualitatively distinct parts.  The form of the living, thus, must be the form of one organism that is a true unity of very diverse parts.[7]

                Third, the operations of living things differ radically from the activities (not really operations) of the non-living.  Here Aristotle gives a partial list.

The term ‘living’ has many senses; but let us say that a thing is living even if it has in itself only one of the following:  the intellect, the power of sensation, the power of producing motion and of stopping with respect to place, the power of moving with respect to nutrition, that of deterioration, and that of growth.[8]

Aristotle had already discussed briefly the fact that living beings must have a certain organic structure, and elsewhere he points out that reproduction is an essential operation of the living.[9]  Aristotle, thus, gives a list that corresponds rather well to a list that one would find in a modern textbook on biology.  The authors who I quoted earlier give six essential operations of living beings.[10]  Specific Organization--the tendency of organisms to have certain parts in a certain order (the fact that they are organic, Aristotle's terms).  This would include characteristic colours, sizes, and shapes.  Metabolism is the general term for all of the processes that serve the growth, maintenance, and repair of the organism.  Metabolism is subdivided into anabolism, the converting simpler substances into more complex to store energy (as fats or carbohydrates); catabolism, the process of breaking down the complex substances for the release of energy and the using up of cellular materials; and growth, an increase in the cellular mass (usually in nitrogen and protein) and a tendency toward organic differentiation.  Movement, something that applies to plants and to animals, and even applies to animals that, like sponges, corals, and oysters, move their environment rather than themselves.  Irritability is a response to stimuli, whether we call the response sensation or some sort of plant movement.  Reproduction is probably the most important characteristic for distinguishing the living from the non-living, for there are viruses which do not metabolize or move, yet because they do reproduce most biologists would allow that they are living.  Finally, Adaptation is the ability of a species to survive by changing to suit the environment.

                This list, with the exception only of adaptation, was insisted upon by Aristotle as the properties of life, that is, as the unique and distinguishing marks of the living from the non‑living.  If it is true that these properties are properties of the living, and if it is true that the properties of the living being are not the properties of physical or chemical beings as such, then there must be some actuality that is not part of the natural physical and chemical make-up of the organism.  That is, the organism must be more than the sum of its physical and chemical constituents.  This is the point that Thomas wishes to make in the Summa theologiae when he argues that the soul is not a body.  The soul, Thomas says, is defined as the first principle of life in the living things that we know.

Now it is clear that not just any principle of vital operation is a soul, for thus the eye would have to be a soul, since it is a relative principle of vision, and the same would be true for the other instruments of the soul.  But the first principle of life we call the soul.  However much a body is able to be a relative principle of life, as the heart is the principle of life in an animal, nevertheless no body can be the first principle of life.  For it is clear that to be a principle of life or to be living does not belong to a body insofar as it is a body, for otherwise, every body would be living or would be a principle of life.  Being alive, therefore, or being a principle of life belongs to a body through the fact that it is such a body.  But the fact that it is actually such it has from some principle which is said to be its act.  The soul, therefore, which is the first principle of life, is not a body but the act of a body, just as heat, which is the principle of heating, is not a body but is a relative act of a body.[11]

Thomas makes two points in this passage.  First, the many bodily organs are each principles in some relative way, but none of the organs of the living body can be the first principle of life.  There must be some principle of organization that makes the whole to be an organic whole.  Second, the reality of a body as such is common to the living and to the non-living.  If a body is alive, it is not because it is a body, but because it has been made to be a certain sort of body.  It has a peculiar sort of actuality not because of something bodily but because of something that has made the body to be what it is.

                Here an objection might be brought against all that I have been arguing in the name of Aristotle and Thomas.  In the light of the Thomistic argument that I have just talked about, could a materialist not seize upon Thomas' last point and claim that it is precisely the fact that the body is such a body, and no other fact, that accounts for the being alive of the body?  There is no need to bring into the discussion a new “actuality”, “form”, or “soul”.  The mere fact that the body is organized in such a way as to be alive is a sufficient explanation for the fact that the body is alive.  Or, to put this another way, the fact that the organs and bodily parts exist in such and such an order is sufficient to explain the fact that the body as a whole is alive.  Being alive, on this materialist or mechanist account, is nothing more than having a certain order among organs, or a certain order among chemical substances in the body.  

                This powerful objection is one that has been met by Richard Connell in his fine book, Substance and Modern Science.[12]  I shall draw upon his discussion in the following.  To say that the living being is alive because it possesses a certain order among parts is to say that the living being is closely analogous to a machine.  A machine does something greater than what its parts can do, for it is a whole that is greater than the sum of its parts, and a machine only can perform its function if its parts have just such an order.  In some ways, it is true, the machine is analogous to the living organism, but in some crucial ways the two cases are not analogous.  For one, there is a great difference between the organs of a living being and the mechanical parts of a machine.  Organs are produced simultaneously with the whole, for they develop while the whole organism is developing, but mechanical parts are made separately from the whole machine and may be made temporally before or after the rest of the machine.  As well, an organ cannot perform its function apart from the organism, as the eye, for example, cannot see apart from the living animal.  Mechanical parts, however, can perform their functions apart from the whole machine.  Or again, organs' functions are determined by the whole organism, whereas the functions of mechanical parts are determined independently of the whole.  Second, machines are passively moved by some motor, agent, or fuel that is outside of them.  This source of motion, whether it is a motor or agent or fuel, can be separated from the machine or can be replaced with some other source, even a source of a different kind.  An automobile can be powered by a gasoline engine, but it can just as well be powered by an electric engine, and if so it would still be an automobile and would perform the same essential function as a gasoline powered automobile.  A living being, by way of contrast, takes in its nutriments from the environment in such as way as to make the formerly non-living materials into a non-separable part of itself.  Anabolism is not a process of storing some material, as fuel is stored in a gasoline tank, but is rather a process of transforming matter.  Third, the coming to be of a machine does not bring into existence new properties (physical or chemical) that were not already present in the parts.  A machine constructed out of hard or malleable parts will be hard or malleable as a result, but the existence of living organisms does entail the new existence of physical and chemical properties.  A vivid example of this is given by Connell.  Most cells are primarily aqueous, and as such ought to have the physical properties of water.  They ought to be shaped like drops, for example.  In fact, however, many cells do not have the drop-like shape; nerve cells, for example, are long and thin.  But when they die they tend to resume a drop-like shape that would be appropriate to an aqueous substance.  The point is that new physical properties come into existence with the coming into existence of the organism--something that does not occur at all with machines.

                The inadequacy of the machine as metaphor for the living can perhaps be seen most clearly when we think of reproduction, even in its simplest form, cell division.  There are two major ways in which reproduction differs from mechanical operation.  First, reproduction does not serve as a tool or instrument for something else.  Machines, by their very meaning, are tools or instruments for human purposes.  A machine does not have any intelligibility apart from its use by some human or at least intelligent agent.  It also makes perfectly good sense to say that a machine designed and made for one end is used by the owner for some other end (as I regularly use my slotted screw drivers for chisels).  We could thus think that the activity of a machine only makes sense in terms of the purpose given to it by its user.  Living organisms, by contrast, do not function for the purposes of some other agent.  If some purpose is to be ascribed to reproduction, it is simply the survival of the species.  Even if we could make self-replicating machines, we would naturally wish to know who or what was to make use of the second and third generations of machines; we should wish to know their purpose in a way that we would not about living species.

                Second, the most basic kind of reproduction, that of cells, occurs by division, but a self-replicating machine does not replicate by dividing.  A machine would use outside materials and mechanical means to replicate, whereas the cell divides with inner materials and by mostly non-mechanical means.  The machine operates on outward parts, and for a machine to divide something would be for one active part to act upon another passive part.  Now to some degree there is mechanical activity in cell division, for the chromosomes, for example, are separated by the spindle fibres of the centrioles, which pull the chromosomes apart.  But the chromosomes do not themselves duplicate in such a mechanical way--their mitosis occurs within themselves.  And the organelles, except for the mitochondria, duplicate by disintegrating in the cytoplasm and by reforming in the daughter cells.  Hence, the division of a cell is a mixture of different sorts of activities.  Some parts reduplicate themselves, some parts are acted upon by other parts in a quasi-mechanical way, other parts disintegrate and are reformed.  The division of the cell is an activity of the whole cell; it is only partially the mechanical activity of one active part upon another passive part.

                Connell makes one further comment on the uniqueness of cell division in comparison to the activities of the physical and chemical constituents of the cell:

A physical change terminates in the modification of a property or properties, whereas a chemical change terminates in a new compound with a new set of properties.  Cell division, however, terminates at neither.  The two daughter cells resulting from mitosis are qualitatively alike and individual members of the same species.  The activity whereby this effect is brought about is what is at issue, and it is sui generis.  There is nothing like it in the categories of physical change and chemical change.[13]

                I have attempted to give here an argument against a reductionism, against the reduction of life to the physical and the chemical.  I have done so for two reasons, one that I do not think that any satisfactory doctrine of human nature can be formulated unless we first meet the challenge of this reductionism.  For if reductionism is granted as true, then human attributes can only be introduced by postulating a soul that is one substance entirely separate from the body which is another substance.  In other words, if reductionism is not refuted, we are forced to accept a dualism or to abandon such human characteristics as intelligence and will.  My other reason is that I do not think that the reductionism is fair to biology itself.  If reductionism is true, then there is no science of biology, for there is no true biological reality.  Biology would have to be a branch of physics or chemistry.  But the plain empirical facts of the matter, known long ago to Aristotle and St. Thomas, and given much richer meaning by modern scientists, is that life is irreducibly unlike the more basic levels of material reality.


St. Thomas More College

University of Saskatchewan

Saskatoon, Saskatchewan

[1] Claude Villee and Vincent Dethier, Biological Principles and Processes (Philadelphia:  Saunders, 1976), p. 12.


[2] De anima  2.1, 412a6-11.


[3] Although certain important qualifications must be made when a reality such as an atom, or its particles, is said to be a substance, for such realities do not naturally exist independently and they cannot be said to be complete in species.


[4] “But actuality is spoken of in two ways, as in the case of knowledge and as in the case of the exercise of knowledge.  Evidently, the soul is an actuality as in the case of knowledge; for sleeping and being awake depend upon the existence of soul, and being awake is analogous to the exercise of knowledge, whereas sleeping is analogous to having [knowledge] but not exercising it.”  De anima  2.1, 412a23-26.  Aristotle's On the Soul, trans. H.G. Apostle (Grinnell, Iowa:  Peripatetic Pr., 1981), p. 19.


[5] Summa Theologiae  1.77.1.


[6] De anima  2.1, 412a28-412b9.


[7] It is on the basis of these first two points, and the other distinctions that Aristotle has made, that Aristotle gives his first definition (a sort of conclusion) of the soul:  “the first actuality of a natural body which has organs.”  De anima 2.1, 412b5-6 (Apostle, p. 19).


[8] De anima 2.2, 413a22-25.


[9] De anima 2.4, 415a24-415b8.


[10] Villee and Dethier, Biological Principles, pp. 31-34.


[11] Summa Theologiae  l.75.1.


[12] Richard Connell, Substance and Modern Science (Houston:  Center for Thomistic Studies, 1988).  See ch. 13, pp. 107-113.


[13] Connell, Substance and Modern Science, p. 115.