When examining the problem of universals (see Problem of universals for an introduction), it's important to recognize a basic distinction between universals at the molecular, atomic and subatomic levels and so-called universals at the macro level. It's also important to distinguish between universal properties (properties shared by a class of objects) and the objects themselves.
At the micro level, in particular the level of molecules, atoms and sub-atomic particles, it's comparatively easy to recognize universal properties and classes of objects sharing those properties. Consider the following examples:
- Simple molecules (i.e., molecules that are not composed as chains or other clusters of submolecules, such as polymers or nucleotides). Examples include water molecules, various salts, various simple acids or bases, various kinds of alcohols, fuels, etc.
- Atoms, classified in the so-called periodic table.
- Subatomic particles, such as photons, electrons, protons, mesons, neutrons, muons, gluons and neutrinos, and, more recently discovered components of protons and neutrons known as quarks. The veritable zoo of particles, along with the discovery of quarks, led to categories of particles, such as baryons (composed of three quarks, such as protons and neutrons), mesons (composed of a quark and an antiquark), bosons (particles that mediate forces [or, more generally, which account for field excitation], which include photons, gluons, gravitons and the Higgs boson [which mediates inertia]), and the various leptons (such as electrons, muons and neutrinos).
[It has been hypothesized that other forms of matter must exist in order to explain the structure of galaxies and other forms of energy must exist in order to explain the accelerated expansion of the universe.]
While these various levels of physics and chemistry are complex and subtle, they have in common rigid classifications of objects according to their properties, the essence of universals.
Above these levels, classification gets gradually more complicated, even problematic. That complication can already be seen in complex chain molecules, known as polymers, which include the biopolymers (such as polynucleotides: RNA, DNA). The classification of polymers covers much of biochemistry. At this level, the shape of a molecule is more complex, due to phenomena such as folding. The number of components in a typical polymer is also variable, so that their classification is based on the types of their constituent monomers. For example, DNA molecules are polymers with constituent monomers which are a special kind of nucleotide known as a nucleoside monophosphate. (For more on this, I can recommend Nucleobase.) Even here, classification is not seriously problematic.
It's when one examines objects at the macro level that serious classification problems begin to emerge. Here, one must revert to categories that define "the ordinary case" and various departures (technically referred to as "deviations") from the "ordinary case".
What, for example, is a human being? Human beings typically have 46 chromosomes in their constituent cells, arranged in 23 chromosome pairs. From here, in the typical case, one can distinguish males from females, with the latter having a pair of X chromosomes and the former having a paring of X and Y chromosomes (where the X and Y classification is based on the shape of the chromosomes as well as their typical gene structures). Exceptions include various types of trisomy, or, more generally, aneuploidy. Nevertheless, even with such exceptions, human features are readily discernible and, in particular, distinguishable from nearby species, such as the great apes.
There are useful categories even in stellar objects, such as red giants, red dwarves, blue giants, white dwarves, etc., as have been classified in the Hertzsprung–Russell diagram. In cases like this, it is a convenience to speak of specific cases, even though they represent a points in a spectrum of classification, with near neighbors tending to have the same descriptive classification. On can speak analogously of sharp vs. mild cheddar cheeses, for example, even though the specific sharpness or mildness [or, for that matter, the "cheddarness"] remains unspecified. In cases like these, subjectivity becomes a more prominent feature of classification and one is less likely to claim "universality" of definition.
A similar issue might have arisen in defining what one means by "human being" if evolution had been gradual, rather than punctuated (meaning alternating periods of stability punctuated by what mathematicians call jump discontinuities) as was proposed by a couple of paleontologists in 19721 . The stability of species over time permits a sense of shared meaning in classifying the whole. This is particularly helpful in defining what it is to be human. It is also helpful, of course, to introduce the twin concepts of free will and individual moral responsibility into such a definition. It then becomes possible to develop a coherent theory of natural law ethics.
Such a theory of ethics is an essential foundation to any system of government that supports a notion of inalienable rights that are inherent to human beings, and not subject to the whimsy of government control. In a philosophical anthropology that denies any fundamental distinction between human beings and other animals no such governmental economy is possible. Indeed, without a fundamental theory of universals, no form of government is stable, let alone just.
We are living in a time when this theory is simultaneously being denied by governments and verified by events.