Every cognitive act is about one or more relations. This about is never neutral, it is committed with an intentionality that points towards a signaled relation. To point is also to orient oneself towards the existing things as presences in the world (ousia, dasein), in relation with one another (Heidegger, 1969).
In Plato’s Fedon and Phaedrus, the problem of the knowledge is placed in what regards its object, being concluded that the response to the problem would have to be found through knowledge itself, but for that, and in accordance with the platonic procedures, it was necessary that one first defined what knowledge is in itself.
In the Menon an exercise of fundamental reflexibility is developed towards defining knowledge, in regards to its origin and nature, but it is in the Book VII of the Republic that a theory of knowledge is developed, whose archetypal operationality still remains in all the Western scientific thinking. This theory of knowledge proposes a cognitive model, in which the knowledge acquired through the senses is linked to the change, which is a configurator of ephemeral appearances, and, because of that, this knowledge is considered an uncertain knowledge, particular and subjective, a knowing of opinion or doxa (Note 1). The true knowledge or episteme, is sought for in an immutable reality, intelligible and supra-sensitive, only accessible to the human intellect.
The Greek terms episteme and logos that mean, respectively, science (true discourse) and discourse, compose the term epistemology. This term still remains, in all the Western thinking, reflexively committed with the Greek matrix in what regards the conditions of truth, consistency, legitimacy and legality of knowledge, that refers it and relates it with the existence and reality of the things.
The Greeks understood and considered reality to simply be that which things were. However, this principle of definition would become more complex and controversial, by the need for the development of the concept itself, from the first causes and first principles of the things themselves, that is, from that which explained the nature of these things, in what regarded their origin, which led to the need to work upon two fundamental notions: the notion of matter (Note 2) and the notion of form (Note 3).
These two notions appeared and were developed in the Greek thinking as two primary epistemological oppositions. The first Greek philosophers and, later on, the atomists, considered the first causes and the first principles, according to matter, while Socrates, Plato and Aristotle considered these same causes and principles, according to form. This division has configured, along the whole Western thinking, the interpretative trajectivity of notions fundamental to the exercise of the reflexive thinking in its relation with the conditions of truth, synthesized in the scientific statements.
Heraclitus conjectured an idea of truth persisting and governing through the permanent change of all the things, that is, an order and proportion that the logos expressed and that constituted a universal explicative pattern accessible to all and that, because of that, should be consensually interpreted.
Parmenides, on the contrary, argued for the existence of a truth inaccessible to the common of mortals, being beyond every aspects and perspectives of the daily experiences, that are linked to change or to opinion (doxa). This truth was only accessible to the pure thought or noema.
One can state that with Heraclitus and Parmenides it was trajected, in the Western thinking, a perspectivic genetics that replicated, in the scientific statements, a fundamental opposition between the senses and the intellect or reason, the first, linked to the change and the experience of this change, as well as to the visibility of this change, and, the latter, linked to what is considered to be invisible, permanent and immutable.
However, and even though the methodological criteria diverged, in each of the two thinkers, Heraclitus and Parmenides wished to access the same permanent order and proportion responsible for the existence of all the things and from which any discourses could be stated as true.
The character of permanence, immutability and indestructibility constituted, thus, the fabric of the notion of truth and of the true discourse which, in turn, were linked to the notion of necessity (agakh, necessitas). Some thing could be considered true only when that same thing was necessarily true. The necessity was defined by Aristotle as that which has to be in that way and cannot be in any other way (Meta., V, 5, 1015a; 1015b).
The notion of necessity signals an idea of permanence that, in turn, places it in relation with the notion of essence, from the Latin essentia, term derived from esse which can mean, as verb, to be or to exist and, as name, the being.
Essence has its Greek correspondent in ousia, noun formed from "to einai" which, in turn, also means to be. In its origin, essence meant, just, being, later on, and through the usage, it came to mean that which is. The accent in the verb displaced itself to the subject (ypokeímenon, subjectum) to which the being is attributed.
Later on, the notion of essence came to coincide with the notion of substance, from the Latin substare (to underlie), interpreted (the notion of substance) as subject and substratum of accidents. In simple and general terms, one can speak of the essence of the substance and of the accidents.
With Plato, the term eidos (Note 4) (eidos or idea) came also to designate that which was understood by essence (or essences) of the things.
For Plato, in the line of Parmenides, the ideas or essences existed separate from the concrete things. According to the author, the corruptible nature of all the things that constituted the world of sensitive experience, made it impossible the access to a true explanation about the things. The true knowledge or episteme should, thus, be sought in a supra-sensitive reality, only accessible to the intellect, that is, in the ideas or intelligible essences.
The theoretical or intuitive nature of the platonic knowledge is associated with an intelligence or cosmic reason, nous, also designated by spirit, related with the ideas or essences, which were considered to be the cause of the nous in the soul, by participation. The operativity of the nous was that of facilitating the access of the human intellect to the true knowledge.
Aristotle, dissolved the nous in a dynamis (potency) and in an energeia (act), criticizing Plato about the theory of the eidos. For this author, the essences did not constitute a subsistent separate from the things, being just their formal cause.
By knowing the things we could also know their eidos. The true knowledge or episteme could be found in them as an energeia or principle of being (esse, enai), by opposition to dynamis, which Aristotle considered as a principle of determinable indetermination, that is, the dynamis could only be determined by the energeia that, in itself, was the determination.
The scholastics interpreted the energeia as a synonym of force (vis), that is, a causal principle of action, belonging to the category of quality. The medieval philosophers called it impetus, Descartes called it quantity of motion, Leibniz and Newton called it living force (vis viva).
While disagreeing between each other as to the locality of the universal essences, both Plato and Aristotle agreed, however, that the scientific discourse could only be considered to be true, when it satisfied criteria of universality and of necessity. Thus, it was imposed as a demand of any scientific inquiry, to find the fundament of any statement of truth or of falsehood, in that which were the first causes and the first principles of the things.
In this way, for there to be discursive rigor, the matter and its forms or essences should be analyzed separately as things that are different from each other, both in terms of their identity as well as of the value attributed to them. The epistemic analysis of one should not interpretatively contaminate the analysis of the others.
The object of the knowledge, its form or essence, meaning and definition obeyed, for Plato as well as for Aristotle, rigorous criteria of adequability and agreement that allowed a general semantics of deductive nature (Note 5) that prolonged itself in Euclides geometry and in Arquimedes’ statics, both based upon a system of axioms that constituted self-evident truths, and upon a system of theorems derived from those same axioms.
The semantic determinism of the Greek scientific discourse generalized itself as an epistemic model until Epicurus, distancing himself from the primitive and deterministic atomism of Democritus (Note 6) introduced the notion of clinamen (declination) as a capability that the atoms have of spontaneously deviating themselves from their trajectories. Thus, Epicurus introduced, in the scientific discourse, an element of irreducible unpredictability, absent until then, with epistemological consequences about that which was considered as criterion of truth.
Note 1 – The distinction between true knowledge or episteme and knowledge of opinion or doxa, the latter considered as inferior knowledge, dates back to Xenophanes. In the poem of Parmenides the sensation or aisthesis regards the appearance or opinion (doxa). The sensation has to do with the perception of the senses (aistheta) that Parmenides excluded from that which he considered as truthful knowledge, which belongs only to the domain of the being (on).
Note 2 – Matter, with origin in the Latin materia, corresponds to the Greek terms: arché (principle); stoichein (element); chora (receptacle); and hyle (materia prima). To explain the nature (physis) and the change of the things, the first Greek physicists or cosmologists conjectured that all things came from one single or several principles (archai), these being considered as substantial beings that existed in themselves and by themselves, such as: the water, the air, the energy or the atoms. Aristotle was the first Greek philosopher to use the term hyle (materia prima) (Meta Z 3, 1029a) as subject of substantial or accidental change, that is, hyle as the first substratum of each thing, or immanent principle, from which some thing comes to the being (Physics, I, 7. 129a; 190b – 192b). Hyle is the indeterminate and the potential principle of the being, opposed to the form, this last considered as actual principle of the being. The term materia prima or hyle was introduced by the scholastics, who added the term materia secunda or deutera hyle. The concept materia prima corresponded to the concept of potential matter (in fieri), and, the concept of materia secunda, to the concept of actual matter (in actu).
Note 3 – The form can be designated by the Greek terms eidos (conceptual form, species) and morphe (real material form).
Note 4 – The notion of eidos, translated by idea, became one of the fundamental concepts of all the Western thinking. Originally, the eidos was that which was seen, the aspect, the appearance or the form, normally designated the form of the bodies. In the time of Herodotus, the eidos and its cognate the idea, that meanwhile started to become common use in the Greek society, assumed the meaning of characteristic property or type. Frequently, the eidos/idea appeared as technical term, linked to the notion of potency (dynamis). The eidos/idea can be considered as a linguistic sign, whose semantic richness guarantees its applicability to a certain variety of contexts without that constituting a loss in its original connotative or denotative value, that is, the identity of its primitive nature as linguistic sign is not lost, despite its adaptive growth. Plato recognized its richness and plurality of senses and vastly applied it in different contexts. Being, however, more important that sense which is projected by its metaphysically substantivated application as subsistent essence in an incorporeal intelligible and incorruptible world. This notion, that constituted the core of the theory of the ideas, has its roots in the Socratic eidos, as subsistent essence of certain modes of ethical behavior. In its set, according to Plato, the ideas constituted the archetypes or models in imitation of which all the things had been done, being, because of that, only them (the ideas), the guarantee of all the scientific knowledge (Sophist, 246b; Fedon, 99e; Parmenides, 132d; Timaeus, 52a). The terms eidos and idea were used by Aristotle with the same meaning that Plato attributed to them (Meta., I, 6, 9).
Note 5 – Aristotle created a theory of demonstrative judgments which he called syllogism, from the Greek sullogizomai which means to bring together. In the formal logic, syllogism means the external signal of the deductive reasoning. In its traditional (Aristotelic) form, it is an inference in which a conclusion is inferred from two premises with a common term and through the elimination of that same term. The inference is always made by means of deductive reasonings, from the Latin deducere which means to extract or to diminish. The deduction is a reasoning through which, from one or more considered propositions (antecedents), one concludes necessarily an unknown proposition (consequent). The notion of deduction is in conformity and agrees with the Theory of the Syllogism of Aristotle. The syllogism is, in terms of its structure, considered the most complete and robust expression of the deductive reasoning.
Note 6 – The primitive atomism was attributed to Leucippus and Democritus. Leucippus has remained as a vague and obscure figure, more being known about Democritus and of his writings. Of the little information that has been gathered, it is conjectured that Democritus must have developed the fundaments of the primitive atomism from Leucippus, these fundaments agreed with the Parmenidean principle that all things had their explicative principle in an immutable and imperishable order, but, these same fundaments, were not in agreement with Parmenides, when these stated that that same order had a material nature that was constituted by solid corpuscles that alternately and eternally collided and repelled each other, in accordance with a regular and determined mechanics, in an unlimited space. These small particles or atmoi were considered the smallest particles of matter, solid, hard and indestructible, different from each other in size and shape and in its relative topological positions, in terms of motion and distance.
