The Substance-Accident Metaphysics must admit of a "Species-Individuum Structure" pervading every being. We already encountered and explained this structure on several occasions. But because it pops up in almost every ontological discussion, it is worthwile to direct ourselves to it once more, especially with respect to the very possibility (or impossibility) of a Substance-Accident Metaphysics. The Species-Individuum Structure was first proposed by Van MELSEN, 1955, Natuurfilosofie (An American edition -- not exactly the same in content as this Dutch edition -- was issued in Pittsburgh, second edition, 1954, The Philosophy of Nature)
The most fundamental method used in the empirical sciences (especially Natural Science) is INDUCTION :
After a number of observations or experiments has been done, something is detected with respect to the individual objects involved. As soon as one has investigated a large number of such individuals or individual cases, one generalizes the results of those findings over the whole range of possible cases, i.e. those results are attributed to all remaining relevant individual cases including those of the past and future. In other words, one expects that every thing will, under every circumstance, behave according to its nature. In this way, for example, one attributes, on the basis of results obtained from an investigation of several pieces of Iron, to Iron as such certain properties, for example (a certain form of) magnetizability, without having investigated all individual pieces of Iron, wherever and whenever existing. So a certain nature is presupposed, from which, in a necessary way, a determined behavior originates, in accordance with this nature (implying, and not contradicting, a different behavior in different circumstances), and this in all (relevant) cases : Each time when we have to do with, say, A (i.e. something with the nature A), we also will have to do with B ( = the behavior of A, corresponding to the prevailing circumstance ), and not with, say, C.
B necessarily arises from the nature of A, under these circumstances. When other circumstances are prevailing, then a different behavior, say, D could be observed. The coupling between the actually observed behavior and the prevailing circumstances originates totally from the one nature A.
This explains why regularities can occur, i.e. complex regularities, in which several different natures are involved, allowing to erect natural laws, which describe these complex regularities generally and in an exact way.
So (the method of) Natural Science first of all presupposes in each thing (each being) a fixed nature, which we could call the "Species" part of the thing ("part" here means an ontological part, which implies that such a "part" is itself not a thing (not a being), but just an ontological constituent). In addition to this ontological part, a second ontological part is also presupposed by (the method of) Natural Science, namely an "Individuum" part (because it presupposes that a particular nature is, or can be, realized in many individuals or individual cases). We shall call this state of affairs the presupposition of the Species-Individuum Structure of every material being. Each being consists accordingly of two ontological constituents, and to express this fact we say it is katallel. Such ontological parts are, as has been said, not themselves things (beings), but make something into a thing (a concrete being). They can neither be separated nor exist on their own.
The Species-Individuum Structure is very general indeed :
It is also valid for non-genuine beings like aggregates. Such an aggregate (like a heap of stones) is, first of all, individual, and secondly it admits of a description with respect to content. This content can in principle be repeated over several individual cases. Although that latter description refers to the species factor of the aggregate, that "species" refers to an extrinsic essence of the aggregate, the latter does not have an intrinsic essence : The individual stones of the heap did not come together (to form the aggregate) on their own account, but by extrinsic agents. In genuine beings the species part refers to an intrinsic essence. So the Species-Individuum Structure pervades all of material reality.
Also in mathematical formulas applied to describe (parts of) Reality, this structure holds, because the mathematician must always make use of symbols : Each time when, say, an X occurs in such a formula, this X has exactly the same meaning (such a meaning could relate to a function, or, generally, to an operator, or to a numerical value). So when a certain value is attributed to (the variable) X, it will have this same value at every location where it occurs within that same formula ( NOTE 1 ). Because, as is now clear, the mathematical formulas, like the concrete things, are subjected to the Species-Individuum Structure, they can mirror (parts of) concrete Reality. However, the fact that mathematical formulas are subjected to the same Structure as the one we encounter in concrete things, only relates to a formal correspondence, because in concrete things this Structure relates to matter, while mathematical patterns (formulas) are as such immaterial. In this way the form-matter structure of material beings is a special case of the more general Species-Individuum Structure.
One could, however, conjecture that the mentioned presupposed repeatability of such a nature, of such a Species part, needs not be a strict repeatability, but just a close approximation, amply sufficient for making generalizations and, consequently, for doing Natural Science. For although the Species-Individuum Structure holds strictly within mathematical models and formulas, it is nevertheless true that those models only pretend to give approximate knowledge, because nothing can be measured exactly. So if the ontological structure of real things corresponds to a close approximation to a (strict) Species-Individuum Structure, then this is already amply sufficient for Natural Science (and its methods) to be possible, as long as the fluctuation remains within the empirical margins of uncertainty prevailing in scientific practice.
But because Metaphysics is not an empirical science, the validity of the Species-Individuum Structure, just as an approximation, and nothing more, does make a difference for Metaphysics. And if Reality turns out to comply only approximately with this Structure, then there is no compelling repeatability of a Species part (a nature) over individual cases, and hence all individuals could differ (albeit often very little) from each other concerning content ( NOTE 2 ).
If the individuals do indeed differ in themselves (even if not detectable by observation and measurement), then in fact a thorough indefiniteness prevails. Because also within the time span of an individual (its 'life time') it is not compulsory to assume that this individual remains the same concerning content during this time span. Also in this case the Species-Individuum Structure is only approximately satisfied, because we now also have to do with 'individuals' dividing (i.e. distinguishing) themselves (from each other), not in space, but in time : They are the here-and-now individuals, or 'semaphoronts'. Natural Science is still possible -- if the (strict) Species-Individuum Structure is sufficiently approximated -- but, strictly speaking (and this we must do in Metaphysics) complete indefiniteness could prevail. And indefiniteness is 'coexistent' with flux ( = continuous change ) and this with 'becoming'. This flux, although remaining within the margins mentioned, will be a random fluctuation. Only then it is coexistent with and equivalent to indefiniteness.
So then the world would be totally dynamic (See the Essay on The Totally Dynamic World), totally involved in 'becoming', and an omnipresent indefiniteness would prevail.
But if the Species-Individuum Structure would indeed be only approximately (to be sure, a good approximation) satisfied, then, this would consequently also be the case with regularities -- which we, often only poorly, describe as 'natural laws'. In Reality then, these natural laws would vary a little bit in time. But in what way would they vary? According to certain laws? And what about these (meta-)laws? It appears that, so doing, we will be involved in an infinite regression, and this is not acceptable.
It is best to cut off this regression already right at the beginning and assume that the processes in Reality proceed according to unchangeable laws (inherent in nature, and which Natural Science attempts to describe), and hence that everything behaves, in principle, in a repeatable fashion. This means that the Species-Individuum Structure will be exactly satisfied. And this result can serve as the basis for a thematically significant statement of a Substance-Accident Metaphysics, i.e. this Metaphysics will indeed be thematically possible.
So the Species-Individuum Structure (SIS), especially when referring to material genuine beings, is the ontological cornerstone of the Substance-Accident Metaphysics, because here we find ontological factors necessarily presupposed by Natural Science, which itself has been vindicated by the many successful predictions of its theories.
The Species-Individuum Structure is -- in the case of genuine material beings -- equivalent to the form-matter structure of such beings, and this is -- as we all know -- itself the cornerstone of the Aristotelian-Thomistic Substance-Accident Metaphysics.
But still an important caveat remains :
Couldn't it be that the supposed Species-Individuum Structure just originates from our (human) way of thinking and conceptualizing, when trying to make sense of the world around us? Isn't it just a cognitive category instead of an ontological (structural) category?
When studying, for example, Nicolai HARTMANN's philosophy concerning the categories of the sphere of real beings (which he explicitly distinguishes from the cognitive sphere), we sometimes get the impression that he (nevertheless) confuses his structural categories with cognitive categories.
What if the Species-Individuum Structure is just a cognitive structure? In that case we don't possess the above mentioned cornerstone anymore.
This is a very hard problem indeed.
It could be that our cognitive apparatus imposes this structure upon Reality in order to make sense of it. But this "to make sense of it" could perhaps only relate to, and be appropriate for, the need for successful survival, made possible in a world that fortunately behaves in an approximately regular fashion, allowing for (albeit approximate) predictions, necessary and sufficient for everyday survival, but not appropriate for theoretical considerations that could lead for example to a consistent and precise Substance-Accident Metaphysics.
In this way it could be that things do not have something in them that is a nature, a nature that is objectively distinguishable from matter and from accidental determinations, in which "distinguishable" here means actually present in the thing and actually separated from other factors residing in that thing.
For the time being I would say that the whole development of an updated Substance-Accident Metaphysics, as undertaken on this website, especially in the Non-Classical Series of Essays, should decide upon our final position in this respect.
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