Substance from a Thomistic point of view is a composite of:
1) Actuality and Potentiality
2) Substantial Form and Prime Matter (for corporeal substances, see below)
3) Essence and the Act of Existing.
Substance, along with accident, is also one of the highest categories (supreme genus) of real being. Traditionally, from a Thomistic point of view, substances where divided into first and second substance, and complete and incomplete substance. First and second substances where categorized by making use of a hierarchical tree (Porphyrian tree). Corporeal first substances (particulars) are individuals and the second substances (universals) are instantiated by individuals. We have come a long way in trying to describe particular substances and how they relate to others and in the process created many taxonomies for various material substances.
Below are proposed Porphyrian trees for substances. The first differentiae is between corporeal and incorporeal substances. Corporeal meaning anything that has a physical, material body or is spatially extended. Incorporeal in turn then refers to something that does not have a body or is physically extended. An argument can be made that the four fundamental forces (weak, strong etc.) are examples of incorporeal substances. From a Thomistic point of view they are still composites of actuality and potentiality and essence and existence even if it is not spatially extended (Figure 1). The fundamental forces of course have no intellect, so incorporeal substances can be differentiated between intellectual (for the moment we leave it as metaphysically possible to have incorporeal, intellectual substances) and non-intellectual. Corporeal substances can be differentiated between living and non-living substances.
The basic characteristic that differentiates living things from non-living things is immanent activity and causation . Following Oderberg’s (1) definition:
1) A living substance is just a substance with the natural capacity or power for self-perfective immanent activity.
2) A living substance acts for itself in order to perfect itself (whatever kind of substance it is) by producing, conserving and repairing its proper functioning.
3) A living substance is able to do 1) and 2) by means of immanent causation whereby the efficient causation begins with the substance and ends with the substance for the sake of the substance. I.e. a substance can be argued to be closed to efficient causation (Louie, 2008) (2).
Homeostasis thus is the hallmark of immanent activity and causation. All living things are capable of performing some sort of homeostatic function and such a function is characterized by 3 mechanisms:
These 3 mechanisms of homeostasis in living things are thus responsible for metabolism, repairing and the potentiality of replication. It is possible for substances to have some sort of homeostatic function without having the potential to replicate e.g. a thermometer. Thus, having at least the potential to replicate is another distinguishing feature of living things.
In a nutshell, livings are differentiated from non-living things by the fact that they are capable of immanent causation and activity, AND homeostasis (metabolism and repair) AND have the potential to replicate (Figure 1).
Figure 1: Substance Porphyrian tree (tier 1-3).
Living substances can then be differentiated between motile and non-motile living substances. Motile living substances are (according to this view) termed as “animals” and non-motile living substances are terms as “vegetals” (Figure 2). Animals can be further differentiated into conscious and non-conscious animals. Consciousness is just the ability to be self-aware and have subjective feelings. Non-conscious animals are tentatively called “critters” on this view. Consscious animals can be differentiated between intellectual andnon-intellectual animals. An intellectual animal is an animal that has the capacity or power to abstract universals from particulars via reason. Such animals are termed “man” and non-intellectual (but conscious) animals are termed “beasts”. Thus, there are 4 essential species which can be further differentiated by their accidents (relational or evolutionary or biological or morphological etc.) into infima species (Figure 2). Living substances are composites of matter and form. On this view, (following the Aristotelian-Thomistic view) all living substances’ form is the “soul“. The kind of form a living substance has is determined by the kind of “essential species” (not infima species) a living substance is. Thus, there are four kinds of “souls” for living things e.g.:
1) Non-animal (vegetal) soul.
2) Unconscious animal (critter) soul.
3) Conscious animal (beast) soul.
4) Intellectual (rational) animal (man) soul.
Figure 2: Porphyrian tree for living substances (click to enlarge).
A Porphyrian tree for non-living substances can also be tentatively constructed from the available information about such substances (Figure 3).
Figure 3: Porphyrian tree for non-living substances (click to enlarge).
Such a view of course is not reductionistic-cum-mechanistic-cum-atomistic. Reality is not described in terms of metaphysical elementary particles that are indestructible and unable to undergo substantial change. Change is not described in terms of the constant mechanical arrangement and rearrangement of these metaphysical elementary particles. Instead, change is described as the reduction of potentiality to actuality and substances are able to undergo substantial change and accidental change. Prime matter is the “support” for substantial change while substances act as the support for accidental change. next then is to differentiate between the kinds of accidents.
1) D.S. Oderberg. Teleology: Inorganic and Organic. Contemporary Perspectives on
Natural Law (2008), chapter 16.
2) A.H. Louie. Functional Entailment and Immanent Causation in Relational Biology. Axiomathes (2008) 18:289–302