“Sharp of taste”: the concept of acidity in the Greek system of natural explanation

Abstract

Acidic substances were known for thousands of years, and their macroscopic-sensory characteristics were reflected by words in most ancient languages. In the Western canon, the history of the concept of acidity goes back to Ancient Greece. In Greek, the word associated with acidity from its early literary references was ὀξύς (“sharp”), and still in contemporary Greek the words “sour” and “acidic” have the same root. This paper makes a short presentation of the appearance of the abstract concept in the works of Plato and Aristotle and relates it, on one side to the already existing theological-philosophical tradition, starting with Hesiod´s Theogony and on the other, to the then available to the Greeks organoleptic experiences of sourness-vinegar and sour milk.

«νόμωι γλυκὺ καὶ νόμωι πικρόν, νόμωι θερμόν, νόμωι ψυχρόν, νόμωι χροιή, ἐτεῆι δὲ ἄτομα καὶ κενόν»

(“By convention sweet is sweet, bitter is bitter, hot is hot, cold is cold, color is color; but in truth, there are only atoms and the void”).

Democritus

Introduction

The human sensory ability to detect sour taste is of course biologically inbuilt and was initially functioning as a protective measure against the ingestion of unripe, spoiled, or dangerously fermented foods (Zhang et al. 2019). While the initial human reflex toward the sour taste must have originally been aversive,¹ cultural habits had been developed toward tolerance and even preference. It is relatively safe to assume that in Asia, such cultural habits have been influenced and encouraged by the discovery, spreading, and cultivation of citrus fruits. Originating probably in southeast Asia (Wu et al. 2018), citrus fruits spread to China, India, and the regions under their cultural influence, affecting the local tastes and presumably leading to the generation of relevant concepts in the respective languages. The Citron (Citrus medica L.) was reportedly sanctified in India, and consecrated to the elephant-headed Ganesh, while the Chinese literature contains repeated mentions of citrus fruits, as early as the Yu Gong text-which was put into writing probably around the fifth century BC but contains much older traditions (Scora 1975). The spread of the plants towards Europe took its time: citron, sour orange, lemon, and pummelo were brought into North Africa and Spain by the Arabs sometime in the tenth or eleventh centuries, and the Balkans might have gotten some contact with lemons a bit earlier. The origins of citrus fruits in east and southeast Asia are still apparent in their names in several European languages. For example, in the Scandinavian languages and several north German dialects the name of the orange is variations of the word apelsin (“apple of China”), while in contemporary Greek it is called portokáli (πορτοκάλι), a memory of the fact that it was transferred to the Greek lands by Portuguese traders. The origin of the word “mandarin” is similar -although historically misleading. The word “orange” is derived from the Sanskrit "naranga", but it might have an even earlier Dravidian origin.

Roughly the same period as the earliest mentions of citrus fruits in the Chinese literature, on the shores of Ionia and the adjacent islands, and subsequently in mainland Greece, a conceptual revolution was happening. In an unexpectedly bourgeois setting, located at the center of an extended trade network and free of direct imperial controls, the city-states of the region were giving birth to the philosophical phenomenon -a historical peculiarity with deep roots in the forms and concepts of the Greek pre-philosophical religious tradition. Active between the sixth and the fifth centuries BC, the Ionian “School” of philosophers (essentially natural philosophers, in contrast to the strands of philosophy that were to flourish in the Hellenistic era)² included virtually all the major names of the Greek thought of the pre-Socratic time: Thales, Anaximander, Anaximenes, Heraclitus, Anaxagoras, Diogenes of Apollonia, Archelaus, and Hippon. Although these thinkers did differ in their conclusions and methods, they did share the main questions and, eventually, developed a thought pattern that shaped Western philosophy and is still influential today.

Theogony and Philosophy: a thought pattern

Around 700 BC, Hesiod's Theogony contained a detailed account of cosmogony, beginning with the primeval Chaos who beget Gaia, Eros, and Tartarus. Then dark and light conditions were born from Chaos, while Gaia in a union with Heaven gave birth to the Ocean. Further on, Heaven and Earth beget the race of Titans, who subsequently gave birth to the Olympian gods. Chaos -the initial non-entity- remains still elusive as a concept: the name might be originating in the root χα- (chasm, an empty yawning space), or was just generated by the poetic imagination. The introduction of Gaia as a matrix of organized matter, and of Eros as a personified force of union, and hence creation, turned Chaos into a describable entity placed at the beginnings of the humanly conceived time (Bussanich 1983). To the Greek word “chaos”, we owe the later invented word “gas”.³

While this account was, of course, non-scientific (and with noted similarities to other accounts of middle-eastern cultures), it did have two important characteristics: on one side, it contained a generative non-personal source of cosmogony (Chaos and not a deity), and on the other, it implied a necessary sequence of events (A, then B, then C) originating on this first entity. Hence, this particular religious text attempted a logical and systematic explanation of the cosmic order, without presupposing the personality and motives of an initial God, while manding from the audience the development of cause-effect relational thought (see Graham 2009). This scheme of Theogony, inscribed in a popular epic that was sung everywhere in Greece and its colonies, provided thus the Greek thought with the first traces of a philosophical cosmogony.

Following this pre-philosophical tradition and its general acceptance, and living in an environment that lacked strictly organized religious structures, it comes not as a surprise that, a century and a half later, Anaximander's account of cosmogony follows a rather similar route. In his account, the original state of affairs consisted of some everlasting stuff -“boundless”, “Apeiron”, should this be- which generated a primordial seed substance that gave rise to qualities like hot and cold. This substance subsequently:

“… broke off and was closed into individual circles to form the sun, the moon, and the stars. (…) in the beginning, man was generated from animals of a different species, inferring this from the fact that other animals quickly come to eat on their own, while man alone needs to be nursed for a long time. For this reason, man would never have survived if he had originally had his present form.”

(Pseudo-Plutarch Miscellanies 2 = A10, reported in Graham 2009).

Anaximander thus articulated the earliest known theory of the evolution of species (including necessarily the human animal) and generated an important philosophical pattern for the subsequent philosophers, which could be viewed as a closed system of natural explanation. In this logical pattern, there is an initial source, out of which everything arises, that is not a personal God. This source is almost always indescribable in human terms, and is quite often perceived as a special kind of matter that has always existed and, quite probably, still permeates the Cosmos. There is a process that generates out of this matter a seed-like formation or stuff that solidifies and self-organizes into known qualities and bodies. This thought pattern had thus a satisfying explanatory function -not only for the genesis of the cosmos but also for its continuous development, the observed qualities, in the past and the future.⁴

While Greek philosophy traversed some other paths after Socrates, natural explanations remained generally compliant with this pattern, and it could even be convincingly argued that the political and ethical thoughts of the Greek thinkers of the subsequent centuries were generated analogically to it -even as late as the Byzantine era. Furthermore, and quite importantly for the history of chemistry, it was on this idea, of the common origin of all the observed elements, bodies, and qualities, that alchemy was later to be grounded. More than a thousand years after Anaximander, Stephanus of Alexandria, seeing the Apeiron as matter´s soul equivalent (and relying heavily on the Platonic thought) wrote:

“It is necessary to deprive matter of its qualities to draw out its soul… Copper is like a man; it has a soul and a body (…) After a series of suitable treatments copper becomes without shadow (…) The elements grow and are transmuted because it is their qualities, not their substances which are contrary.” (mentioned by Pattison-Muir 1902).

Hence the observed qualities -also those of taste- and their perceived differences are emerging properties of different organizations and forms of the underlying apeiron. In such a worldview (and all its variations) it would be conceivable that sensory qualities that seem similar, interrelated, or exchangeable, would be the manifestations of similar underlying conditions and forms. This applied strongly in the case of taste: in the culture of antiquity, and well into the early modern era, the taste of things was perceived to have ontological bearings. It had to be a testimony of what the things are and had epistemological implications (Shapin 2011). As late as the nineteenth century, taste and odor were decisive factors for the identification and classification of substances, and taste as an important factor for the development of science is currently being reevaluated by historians (Hendriksen, Wragge-Morley 2022).

Oxos and oxygala

While citrus fruits appeared in the Mediterranean late, and after the Greek philosophical canon was formed, vinegar and fermented dairy products were present quite early and were used extensively. Hence it was these products of fermentation that gave Greek philosophers the paradigmatic sensation of sourness, and, in the Greek canon, their taste is the one employed as an example.

Vinegar would have been discovered naturally a little bit after humans learned of the uses of alcoholic fermentation, and is attested in Babylonian sources: the Babylonians were preparing acetic acid solutions from the juice or sap of the date palm, from date wine and raisin wine, and beer (Conner and Allgeier 1976). Although vinegar was generally not considered “food” among the peoples of the ancient world -it does have extremely low nutrient value, after all- it was widely used as a condiment in food, as a preservative and a pharmaceutical, or, in the verified case of the Greeks and the Romans also as a constituent of popular drinks (generally thought, however, as drinks of the poor, the masses, or the soldiers). In ancient Greece, one of the drinks of the masses was Oxycrat: a mixture of vinegar, water, often wine, and honey.⁵ For long-distance trade of agricultural products, vinegar was of immense importance as a preservative, so it is safe to assume that a form of artisanal industry developed around its production quite early.

Fermented dairy products on the other hand have an origin that goes back to the beginnings of animal domestication, the agricultural revolution, and the earliest steps of the civilizational phenomenon: indeed, it could be argued that, without their (most probably accidental) discovery, a great part of this revolution would have been impossible. All early civilizations developed husbandry methods and the production of types of fermented milk -less due to culinary preferences, and more due to the need for storage, transport, and trade of the produced surpluses (Bintsis and Papademas 2022). Soon enough, ancient populations acquired the taste of sour dairy products and discovered that such products have special nutritional value -alleviating for example the symptoms of lactose intolerance, or assisting with digestion (Curry 2013). The people belonging to the ancient cultures could see the double irony, more than moderns ever could: while acidity (using modern terminology) comes as a result of the corruption of valuable products, the products of this corruption are enriching the organoleptic experience and are indispensable to cleanliness and conservation.

In the Greek society, both vinegar and sour dairy products received special positions, affected nutritional habits, and proved to be quite persistent: the majority of the products attested in the literature of the classical era are still usually consumed in Greece two millennia later-and the words used for their naming are still in use, either the same or slightly altered. In Greek, the word associated with acidity from its early literary references was ὀξύς (“sharp”), and still in contemporary Greek the words “sour” and “acidic” have the same root.⁶ The word ὀξύς, according to the Liddell-Scott-Jones Lexicon refers both to the sharpness of a point and the sharpness of an edge.⁷ Early on, the word was associated with common sour products: oxos (vinegar, made primarily out of wine) and oxygala (sour-fermented milk). While it is hard to know for certain, the ancient Greek oxygala is most probably the same product that in today´s Greece is known as xinogala (Alcock 2006).

Plato´s and Aristotle´s “sharp of taste”

In Timaeus, Plato is comprehensively presenting his version of the thought pattern that we have already seen by Anaximander in the introduction, and all the natural qualities discussed are artfully inscribed in this pattern. Plato´s version is, of course, a top-down one: the initial disorderly state of affairs in the “receptible” (“δεξαμενή”, “third kind”, “τρίτον γένος”, presumably the equivalent material substratum of the chaos-matter of Anaximander) is organized by the word of a Demiurge (a “creator” or a “craftsman”), building up thus an ancient bridge between philosophy and cosmogony on the one side, and handwork, art, and craftsmanship on the other, that shall be inherited by alchemy in the subsequent centuries.

While the discussion whether the cosmogony described in Timeaus should be taken as an allegory or not (and whether it is really a “creationist” account-since the appropriate vocabulary for a purely materialistic description of the birth of the universe was lacking at the time), few facts are fairly clear: the platonic universe is perceived there as a living thing, containing a perfect soul that permeates all; it possesses Intelligence; and it has a shape -quite understandably, a sphere. Before the intervention of the Demiurge, goes the story, the substance that will become the Cosmos contains only traces of the four elements (fire, air, water, earth), which are made up of geometrical three-dimensional bodies (respectively, tetrahedra, octahedra, icosahedra, and cubes). The elements as such begin existing, only after the master Craftsman puts the aforementioned traces together, forming elementary (literally) corpuscles. The elements find then themselves in perpetual motion: corpuscles of the same kind being attracted, but never separating into pure forms completely because of the limited space offered by the enclosed cosmic sphere. The formed corpuscles then and their motions and exchanges are the underlying reality of the perceived phenomena.

Plato had the sensory experience of vinegar and sour milk in mind when he was writing:

“… Again, when particles already refined by putrefaction, entering into the narrow veins, are symmetrical with the particles of earth and air contained therein, so that they cause them to circulate round one another and ferment, then, in thus fermenting they change round and pass into fresh places, and thereby create fresh hollows which envelop the entering particles. By this means, the air being veiled in a moist film, sometimes of earth, sometimes of pure moisture, moist and hollow and globular vessels of air are formed; and those formed of pure moisture are the transparent globules called by the name of “bubbles,” while those of the earthy formation which moves throughout its mass and seethes are designated “boiling” and “fermenting”; and the cause of these processes is termed “acid.”…”

(Plato, Timaeus 66a-b).⁸

Although this mention of acidity as a taste-related property is notoriously difficult to translate and interpret, it does demonstrate the effect that vinegar and oxygala had in the generation of the concept. Plato related the sour quality with putrefaction and fermentation: according to his experience, the property in question was observed primarily in substances that were left to corrupt (even when that was done intentionally). Furthermore, he could not help but relate the appearance of the property with the formation of “bubbles.” If we wanted to interpret, we would say that Plato says that acids are substances that are formed by fermentation, when particles are found enclosed in films of moisture that enclose air.

It is worth mentioning that the word used for acid is the word ὀξύ-and this word is characterized as a “cause.” The original text (“… τὸ δὲ τούτων αἴτιον τῶν παθημάτων ὀξὺ προσρηθῆναι “) can only loosely be translated as “and the cause of these processes is termed “acid.” The word πάθημα means “that which befalls one, suffering, misfortune”, and, by extension, change that is forced by external action.⁹ Plato then is designating an active character to the “cause” acid (αἴτιον) and a passive to the process that leads to its appearance, placing thus the idea “acid” ontologically before the manifestation of the acidic properties. Hence, in Timaeus, one finds an early example of acidity as an abstract concept and a natural category, which can accommodate numerous observed phenomena.

The use of the word ὀξύ (“sharp”) and the relation that this word has in the Greek language with the sharpness of the points and edges of blades, had led over the centuries to interpretations that relate Platonic acidity to the microscopic properties of Plato´s corpuscles. As Nicolas Lemery was writing in 1675:

“I hope no body will offer to dispute whether an acid has points or no, seeing every ones experience does demonstrate it, they need but taste an acid to be satisfied of it, for it pricks the tongue like any thing keen and finely cut.”

(Cours de Chymie, reported in Ruthenberg and Gerontas 2018).

Such interpretations, while plausible (and, indeed, historically fruitful for the development of chemistry and medicine), should be handled with caution. Plato was not the creator of the term for the description of the sour taste-it seems that this use of the word was usual in the everyday Attic dialect of his time. Hence, we may assume that the term preceded Platonic atomism. Whether Plato saw any relation between “sharpness” in taste and the “sharpness” in the form of some microscopic particles is unclear.

While Plato took the course of identifying a category of acid that could be employed to cover more than one phenomena, Aristotle had other preoccupations. Acidity does make an appearance in his Meteorology (Μετεωρολογικά) but in a second role. In this work, Aristotle initially attempted to present and explain the interrelations between observed changes in earth, air, and water -generating the term meteorology in the process.¹⁰ The Aristotelian universe consisted of the same four Platonic elements, and a great part of this work is dedicated to explaining how the multitude of sensory phenomena are generated by interactions of only these four.

What is the origin of the sea, and how can one explain the salinity of seawater? How is it possible to have waters of different tastes? These are the questions posed by Aristotle in the relevant chapter.¹¹ We meet acidity at 359b:

“… Most salt rivers and springs must have been hot once. Then the primal fire in them was extinguished but the earth through which they percolate preserves the character of lye and ashes. Springs and rivers with all kinds of tastes are found in many places. These different tastes must in every case be due to the fire that is or was in them, for if you expose earth to different degrees of heat it assumes various kinds and shades of taste. It becomes full of alum and lye and other things of the kind, and the freshwater percolates through these and changes its character. Sometimes it becomes acid as in Sicania, a part of Sicily. There they get acidic and saline water which they use as vinegar for some of their dishes. In the neighborhood of Lyncus, too, there is a spring of acid water, and in Scythia a bitter spring. The water from this makes the whole of the river into which it flows bitter. These differences are explained by a knowledge of the particular mixtures that determine different savors…”¹²

Salinity is a side-effect of the extinguishment of primal fire in rivers and springs that were once hot. When earth is exposed to different amounts of heat, it assumes different kinds of composition that transfer different tastes to the water that flows through this earth. Read from a modern chemical perspective, the Aristotelian view is a step toward chemical reactivity-through heat-and a recognition of the possibility of complex mixtures of products. The water in Sicania is flowing presumably through more than one earth types, becoming thus of a mixed nature: salt and acid (ὀξάλμη); the water in Scythia is clearly bitter, corresponding thus to one type of earth. This view presupposes the acceptance of these concepts of taste as natural categories, in the Platonic sense. It is worth mentioning that Aristotle in this passage uses the word διήθησις (filtration, percolation) for the description of phenomena of fluidity, and gives filtration a central position for the acquirement of water characteristics.¹³

Concluding remarks: developments and survivals

Next to the Platonic tradition of abstractions and ideas and the Aristotelian elements and proto-reactionary transformations, the contact between Greek philosophy and Egyptian technique generated a new tradition in the Hellenistic era. Alchemy inherited the concept of acid from Platonic thought. Plato´s concept was flexible enough to accommodate first the acidity of the citrus fruits, and later the mineral acids, out of which nitric acid seems to have preceded the rest (Karpenko 2009). Sulfuric, nitric, and hydrochloric acids were of course sharp enough, albeit more intensely and differently than the organic acids known to the classical era. Their discovery -coupled with the transmission of Greek and Arabic texts-generated the European branch of Alchemy, which was to prove rather fruitful. Especially the fourth book of Meteorologica was to play a crucial role, affecting the European understanding of the relations between matter and form for centuries.

The thirteenth century had been a turning point in this process. The conquest and plundering of Constantinople by the Crusaders of the Fourth Crusade opened to the West an unimaginable wealth of Greek texts, coupled with the necessary personnel for their translation and interpretation. The conquest gave also access to Byzantine alchemical practices. While the most famous product of the Greek Alchemy of the Middle Ages was, of course, the “Greek fire”, invented by Callinicus of Heliopolis in the seventh century, the alchemists of the Eastern Empire had other major advances to show. Above all, they had done the heavy work of systematization of the available knowledge (Viano 2018).

The initial description of acids as “sharp” survived long, and intertwined interestingly with the rebirth of atomism in the early modern era. As mentioned earlier, several interpretations of the Greek word for acid and the Platonic message saw a relation between the sharpness of taste and some microscopic reality. By extension, several thinkers of the iatromechanics persuasion were certain that toxicity too was the macroscopic manifestation of even “sharper” corpuscles. Reportedly, anatomical studies of the eighteenth century confirmed this hypothesis by discovering lesions on the internal organs of poisoned subjects.