When studying human thought and language, thinkers, since ancient times up to the present day, have had the intuition that their symbols are ordered in several strata in a way that resembles the living beings division in genus, species, and individual. I use “symbol” and “symbolism” to refer to all kinds of categories, concepts, words and signs. Philosophers name “categories” the deepest stratum of symbols whose presence canalises what people mean. As all genera, they contain species, but, being ultimate, they, in their turn, are not species of some higher genera. Clearly then, to understand the way we think, it would be difficult to examine another problem more important than that of establishing the categories of thought and their origin. Yet (I have got used to making this complaint) the problem of categories is not examined by philosophers as often as it ought to be.

In order to have some examples of categories, let us remember briefly some of the main sets or tables. All of them are designed to be complete, i.e. every natural entity is supposed to belong to one, and only one, category. Among the many eminent merits of “The Master of Those Who Know” (as Dante called Aristotle), mention must be made of the fact that he was the first to discuss systematically the problem of categories, and listed ten: substance, quantity, quality, relation, place, time, posture, state, action and passion.

For Descartes, everything is either mind or matter. Life does not exist. This sharp classification makes it clear that if a property is an aspect of entities belonging in one category, it cannot determine entities in any other category. For instance, colour belongs exclusively to matter-extension and not to mind. It would be impossible to exaggerate the importance of this Cartesian division of reality for the entire subsequent history of philosophy and science up until now.

Kant believes that there are four groups of three categories. Quantity includes unity, plurality, and totality. Quality covers reality, negation and limitation. Under relation: inherence and substance, causation and dependence, and reciprocity between agent and patient. Finally, modality includes possibility, existence, and necessity. Schopenhauer reduced them to just one great category: causality. These tables of categories are the most important proposed by thinkers.

My own set contains four categories. To causality, I would add the concepts of stable object or substance, space and time. If, as I will say later, the origin of language is causal, it is not surprising:

  • that causality is one of the major natural categories: its presence produces the order of reality;
  • that the originality of human language lies in its capacity to express causal relations;
  • it is not surprising that, thinking inductively, we can have an idea of the past and of the future due to nature’s uniformity: approximately the same causes produce approximately the same effects by translation in space and time.

The aim of this outline on the origin of categories is to argue in favour of their natural source. I consider then the two main points of view on this problem: idealism and realism. These doctrines have multiple meanings, and, consequently, multiple are their oppositions too. To fix the ideas, let us distinguish, in an almost Cartesian or Kantian way, between mind and nature, or, let us say, between thought and reality. Thus, for the idealist, categories are constructions of the thinking mind imposed on natural reality, and natural things are intelligible inasmuch as they lend themselves to be structured and ordered by our mental categories. For the realist, on the contrary, form, structure, causal order, and so on, exist in pre-conscious, pre-human nature, before existing consciously in our minds. Thus, the origin of categories is not mental or ideal, but natural or real.

At this point, it is necessary to fix the meanings of some key terms. I call “traditional or partial naturalism” the doctrine that if something is natural, real, then it can be fully described and understood with the formal and methodological tools of physics and chemistry. It follows that the psychical, conscious, and social events are not natural activities — they are condemned to be unfathomable mysteries. I call “integral, comprehensive, true naturalism” the doctrine according to which the entire realm of reality is natural, conscious and social events included. Thus thought, and the systems of symbols that allow us to imagine, remember, and express intuitions and ideas, are real events naturally developed. Since natural categories cover the entire reality whatever its mode of being is — mathematical, physicochemical, biological psychic — they exist also, in a derived way, in our minds.

If categories exist first in pre-psychic nature and only afterwards, in a derived way, in our minds, this means that we obtain them by intuition. Intuition is here a key concept. It means that our consciousness or psychic apparatus is capable of grasping directly and immediately something external to it. As it happens usually in philosophy, this concept can be interpreted in an idealistic or in a realistic way. I retain the last one. Thus, for instance, the categories of stable objet, causality, space, and time, structure the animal and human organism and behaviour since birth. Notice that without the assimilation of those four categories, no living organism, plants included, could survive.

In what follows I take into account both categories and language. Consider that when people see in highly theoretical concepts an argument against realism, what they imply is that language in general is not as natural an activity as realists take it to be, that human categories are more conventional or arbitrary than necessary. It follows that a way of preserving in realistic hands the territory idealists would like to occupy, consists in restoring the necessary biological and physical origin of language. This can be done by going back to the original or natural sources of our categories, a strategy opposed to that which pays attention, almost exclusively, to the highly sophisticated development of language, that is, to the language at work, for instance, in science, literature and philosophy. “I think that the arbitrariness lies wholly in the words and not at all in the ideas”, says Theophilus to Philalethes (G.W. Leibniz, New Essays on the Human Understanding).

Nobody, except of course some analytic philosophers, believes today, as Cratylus did, that the study of words is the science of things (without qualification), and we smile at the idea that to show that language has a natural origin means to show that every word imitates a natural object or being, as some ancients believed. (It is true however that at least some words were originally imitations of some real properties of things, or expressed man's spontaneous or instinctive reaction to them. Notice the physical and geometrical similarities between the utterance of the word "cave" and a cave). It has been pointed out that, at the origin, language is poetical and mythical. We can imagine that Selene provoked a different aesthetic experience from the one suggested by Moon or Luna. Now probably sometimes the meaning of a name is a partial description of (or reaction to) an aspect of a thing, and so there is maybe a residue of truth in Cratylus' program after all.

Language has an empirical origin, but it is not the only one: it seems to have also an abstract or general origin. For centuries, people (among them, A. Smith) have argued that a name is first given to a particular object, then generalized, while others (for instance, Leibniz) think that a particular object cannot receive a name unless a general idea, associated to a phonetic expression, exists beforehand. Still others (Husserl, Russell) do not see how logical truths could be obtained by empirical generalisation. The problem of the origin of language has many aspects and a long history, and we can find information and partial support for contradictory theses. As I said before, what interests me now is to make plausible the idea that the fundamental categories of thought (there is some consensus among the different tables presented) have a natural origin, and reduce, as much as possible, the arbitrary or conventional parts of language.

Returning to Aristotle, we realize that he was right in deriving categories from natural language because it allows us to live. How could an animal live or learn anything if it were incapable of fixing in space and time the presence of other animals and significant objects, if it were incapable of transmitting vital information to its fellow creatures? That is why no table of category makes sense unless it contains at least substance, causality, space, and time. Before becoming a sophisticated means for abstract thinking, language is there to communicate vital information concerning hunger, thirst, fear, search of mate. Cry, mimic, and gesture make up the first language of children. It is then reasonable to suppose with R. Thom that one of the most urgent functions of language was the description and representation of processes in space and time, hence the importance of geometry for understanding the functioning of language.

R. Thom points out that the main syntactic structures come from the formal structure of the major interactions of biological regulation. The biological predatory practice is a prototypical example of transitive action ("the cat eats the mouse"). The universal, for a realist, exists in extra-human nature before existing explicitly and symbolically in conceptual language. On the contrary, the nominalist tends to think that extra-human reality is composed exclusively of particulars, and that universal concepts are useful mental, fictitious devices, to deal with particulars: a universal concept does not represent a universal property of nature.

If we see man like other animals, i.e. as an entity trying to live and survive, then it becomes possible to consider the origin of language from a naturalistic point of view. Man is a natural product living in a natural environment. Their relations leave marks on the organism. I use “mark”, “trace”, or “imprint” to underline the natural beginning of symbolism. The naturalistic idea of the origin of language is then the intuition according to which every symbol is derived from those marks or traces. Every objet “touched” by natural entities, activities, and process reacts to them according to its constitution, motivations and goals. Now, of course, not all traces become symbols. The reason is that an extremely high number of physical entities and process touches our organism, yet most of them are not significant for us, or for the animals concerned, given our constitution, motivations, and goals. Vision, for instance, is a kind of gift that gives us many data we do not really need.

The existence of abstract concepts is not an argument against my naturalistic view of the origin of categories and symbols. I take “abstract” in the naturalistic, realistic and Aristotelian sense of “separating in the intellect what, in reality, is united”. This is, for instance, how mathematics began. In reality objects have mathematical properties. There are round objects, but it is possible for the intellect to consider roundness separately, as if it were an object. In addition, it becomes possible to define a circle — symbolically — in such an ideal, artificial way, that it does not exist at all in the real world. Therefore, Plato and the Platonists imagine an inexistent, unnatural, fictitious world where mathematical “entities” inhabit. After the correct Aristotelian conception of the natural foundations of mathematics, this science, or art, grows by multiplying the levels of abstraction without stopping.

In sum, my naturalistic, realistic, and causal intuition concerning the origin of categories and symbols can be encapsulated in the following principle:

Each time we examine the origin of a category, concept, word, formal sign or linguistic rule, whatever its place in the hierarchy of symbols, let us consider it as a nearby or distant effect produced by the causal imprint of significant things on our organism.