We have followed Ray's idea of distinguishing between the real essence and the classificatory species to Kant's ideas on the scholastic and the natural system. In Ray's theory there are relationships between the essence of a living form and its traits that lead into epistemologically significant problems. The essence lies somewhere "behind" the traits meeting the observers' eyes and guiding their ordering of the phenomena. In one of its meanings this "behind" covers a causal connection between the invisible essence and its manifestation, the phenotype. This connection is the key to understanding the essence itself.
Since only similar traits and functions flow from a particular essence, the fact that several individuals share the same habitus can be interpreted as an indication that they also share the same essence. Such likeness in habitus, texture, and appearance is the sufficient guarantee for identity of essence; the possibility, however, that an isolated trait can be considered essential is deemed improbable.
The concrete, visible overall habitus of the living creature is the expression of a unity working in the background and itself remaining invisible. In this contrast we find the same problem dealt with in contemporary biology under the heading of gene structure and the traits expressed in the phenotype. In both the phenotype is determined by a causal factor whose qualities cannot be seen but must be deduced.
This causal analysis ultimately leads, as we see in Woltereck's work, beyond the sphere of material determination to the reaction norm [Reaktionsnorm] as the determining "inextensive diversity"—that is, an entity that can no longer be comprehended by means of mathematical-scientific analysis and thus leads us back to the living unity as one we have "seen" with our eyes.
We find the ambiguity inherent in the concept of the reaction norm also in Ray's concept of essence. Just as Woltereck's reaction norm is the causal determinant of the phenotype and at the same time because of its inextensivity leads us back from the causal analysis to the reality of organic essence accessible to intuitive perception, so Ray's essence also signifies both the cause of the organic form and its host of traits and the seen being of the living creature, which guides the selection of traits with which the living being is to be described "essentially," "naturally" (in contrast to the scholastic classification according to arbitrary traits that are irrelevant to the natural subdivision).
In discussing this problem, Ray arrived at formulations we will hardly find in modern biology but meet with in the humanities in the typology of Max Weber and Georg Simmel. The total habitus characterizing the living being must be conceived of in the concept of the type, and according to Ray this concept of the type is legitimately formed even when the individuals subsumed under it differ quite significantly from each other in various traits.
The traits are selected on the basis of an immediate grasp of the object, and the selected group is considered "typical," while other traits and groups of traits may be ignored as being "inessential" and should not be considered characteristic. The formation of types thus is the result of a value-based selection (in the sense of Heinrich Rikkert's logic of history), which in this case means: a selection is made in which the guiding "value" is the directly grasped vital essence of the plant.
The "ideal type" so arrived at does not comprise a group of traits an individual absolutely must possess to be considered a member of the type; rather, the traits are ordered with a view to the concrete essence. The empirical specimen may be more or less close to the essence, and perhaps no individual ever fully attains this essence. That does not make the type formation orientated to the concrete essential unity any less legitimate.
In the eighteenth century and in biology, this problem of the visibility of the living essence found its classical expression in Goethe's statements on osteology. According to Goethe, in establishing the type, we are assured by the nature of the undertaking that our procedure is not merely hypothetical, for in looking for laws according to which living, separate beings, acting out of themselves, are formed, we are not getting lost in vast breadths but are being taught on the inside. That nature, when she wishes to produce such a creature, must concentrate its greatest diversity in the most absolute unity is evident from the concept of a living, definite being, separated from all others and acting with a certain spontaneity.
So we consider ourselves already assured of the unity, diversity, expediency, and lawfulness of our subject. If we are now circumspect and strong enough to approach our subject with an imagination that is simple yet wide-ranging, free yet guided by its own laws, lively yet regulated, to observe it and deal with it; if we are able to meet the certain and unambiguous genius of creative nature with the complex of spiritual powers we usually call genius, but which often produces very ambiguous effects; if several persons could work on the enormous subject with a common purpose; then surely the result would have to be something we as human beings should delight in.
Ray's theory of the living unity and its essence contains the full scope of the speculative problems—the scope that allows them to be carried to the poles of Kant's causal analysis in the natural method and Goethe's biology that sees the essence itself.