Socrates first discovered the concept, or eidos as the relation between the particular and the general and as a germ of a new meaning of the general question concerning being. This meaning emerged in its full purity when the Socratic eidos went on to unfold into the (transcendental) Platonic "Idea." (see also essence) The eidos is absolutely and eternally real, but in respect to each single realization, it is the possible, its potentiality. 

Plato and Euclid developed an indissoluble partnership between geometrical and philosophical ideas of truth. The Platonic concept of the theory of ideas was possible only because Plato had continually in mind the static shapes discovered by Greek mathematics. On the other hand, Greek gemetry did not achieve completion as a real system until it adopted Plato's manner of thinking. (see Ernst Cassirer, The Problem of Knowledge.) The concepts and propositions that Euclid placed at the apex of his system were a prototype and pattern for what Plato called the process of synopsis in idea. What is grasped in such synopsis is not the peculiar, fortuitous, or unstable; it possesses universal necessary and eternal truth.

For Aristotle, the problem of the concept is transformed into the problem of teleology. Amid all the multiplicity and particularization of empirical becoming, there emerges something universal and typical, which gives this becoming its direction. The world of " Forms" does not stand beyond phenomena as something prior to and separate from them, but is immanent in the phenomena as a whole of teleological forces, which rule and guide the consummation of purely material events. For Aristotle, the eidos of an identity or process is its organizing principle. Form in nature is not a separate, self-subsistent absolute. It exists only in that which it informs. Within the Aristotelian system, it is the concept of development (of natural or organic motion) that reconciles the oppostion of eidos and hylematter and form, of the particular and the unversal. The Aristotelian entelechy thus signifies the fulfillment sought earlier in the Socratic eidos and the Platonic Idea. (Cassirer, Kant's Life and Thought, p. 277) 

note: The Aristoteleian usage of the concept of eidos also signifies species.

In Neoplatonism, which in general is intended to be a union of fundamental Aristotelian and Platonic ideas, the archetypal (divine) intellect does not take up into itself something lying outside, but produces the object of its own knowledge. Plotinus gave this way of thinking the name " intuitive understanding," which sees the total form of the actual, because it actively produces it each moment and because it is immanent in the formative law which underlies all existence. Development is connected above all with the phenomenon of organic life. (in the metaphysical guise of emanation) Here emerges for the first time in the history of philosophy the relation and distinct parallelism between biological and aesthetic problems, between the idea of organism and the idea of of the beautiful. (Agamben) See organicism . 

The necessity of the transcendental, the impossibility of every form of immediacy, is the leitmotif of Kantian transcendental philosophy. For Kant, "a transcendental principle is one by which we think the universal, an a priori condition under which alone things can become objects of our cognition." (Critique of Judgement, p.17) Kant summarized his epistemology thus: The conditions of experience are at the same time the conditions of the objects of experience -- by which he meant that the process that we call experience and the representations that form its content and objects are subject to the same laws of the understanding. 

For Cassirer, the essence of idealist aesthetics lay in the relation between the pure world of forms to the world of appearance through the formative logos. In this view, the work of art is only one particularly notable specimen of that "inner form" on which the cohesiveness of the universe as a whole rests. see Critique of Judgement. (see also style.) 

John Locke distinguished between the "nominal essence" and the "real essence." The nominal essence is that set of properties whose manifestation is necessary for a thing to be identified as of a certain kind, in order to name the thing. The real essence is the nature of the thing, conceived as the "hidden" structure which causally accounts for its manifest properties and provides the choice of criteria for individuation and identity.

For revisionist Biologists like Brian Goodwin and Gerry Webster, the organism and its parts must be thought as "powerful particulars." If their real essence is to be equated with the causal mechanisms responsible for the production of manifest morphological characteristics, this essence must be sought in the morphologically relevant structure of the organism and its parts.

what is "eidetic thinking" ? (see geometry for "eidetic sciences")

In the 1860's Franz Brentano developed the doctrine of intentionality, which he also called "immanent objectivity." This is the idea that all experience involves directedness towards an object, that every mental phenomenon includes something as object within itself. About these objects we can have certain and not merely probable knowledge. In his early work, the Logical Investigations of 1900-1901, Edmund Husserl described phenomenology as a "descriptive psychology." But by 1904, he had retracted this definition in favor of a "transcendental phenomenology." 

Wilhelm Worringer's accounts of abstraction identify the psychic function of abstraction in art with the aims of transcendentalism in religion -- "to translate the mutable and conditional into values of unconditional necessity." (appendix) 

Deleuze and Guattari seek a thought-in- becoming, which is entirely immanent, not to develop a general idea (model) that would stand out and above (transcend) the bodies its subsumes. (see plane of immanence) Deleuze and Guattari stress the reality specific to becoming. They characterize becoming as intransitive, not having an object of production other than itself. "Reality makes and remakes itself, but it is never something made." Deleuze follows Spinoza in his explorations of an immanent cause -- one in which it is impossible to distinguish between the action and the agent, in which the grammatical categories of active and passive, subject and object, transitive and intransitive lose their meaning. Michel Foucault echoes this position when he states that " Power must be understood... as the multiplicity of force relations immanent in the sphere in which they operate and which constitute their own organization; as the process which, through ceaseless struggles and confrontations, transforms, strengthens, or reverses them." (History of Sexuality, Vol 1, p. 26) Deleuze calls the "diagram or abstract machine ... the map of relations between forces, a map of destiny, or intensity, which...acts as a non-unifying immanent cause which is coextensive with the whole social field. (see also desire ) 

Transcendence, for Deleuze and Guattari, is vertical Being, imperial State in the sky or on earth, where there is religion. Molarization involves the creation of the plane of transcendence (also called the plane of organization.)

Simone de Beauvoir saw the split between transcendence and immanence as the great divide between the sexes. Women were trapped in immanence while men could heroically struggle for transcendence. Ideal love was for women a way to vicariously experience male independence while submitting to it. (see sex / gender )