In this contribution, I argue for epistemological impurity as the key to the historical reconstruction of the proto-biological sciences of the eighteenth century.

The traditional approaches to the more or less complex and more or less stratified past of science either focus on the ideal content of that which has in the meantime been recognized as standard biological knowledge (transmitted from generation to generation by textbooks) or otherwise try to uncover the implicit cognitive principles at work in order to reveal their shortcomings (as measured against today's accepted criteria = epistemological presentism).

A closer look at the breakdown of the classical models of mechanistic explanation and the detailed analysis of the new empirico-experimental research in the neurophysiology of the eighteenth century shows, however, that eclectic procedures of various kinds have dominated the field. This eclecticism (the principle of epistemological impurity) supported, and was in turn supported by, what has recently become known as “thinking with one's hand.” The paper illustrates this specific kind of thinking (and experimental acting) with reference to the case of Nicolas Le Cat's microphysics of nervous activity.

This name is given to any collection of similar individuals of the same nature which exist, although we can observe only some of these individuals, and never the entire collection of all at the same time.

Elkana's paper “Two-Tier Thinking” (1978) contains the thesis that became the foundation of all his later work. This thesis is best summarized by the author himself:

The thesis of this paper is that this distinction [between realists and relativists] is not a logical necessity but a historical situation in Western scientific culture. It is claimed here that the distinction is spurious: every problem has a realist and a relativist dimension, and the two views can be, and are actually being, held simultaneously. Once a frame of reference has been selected, in it realism prevails. With respect to selection of an appropriate framework the approach has to be relativist since there is no absolute, external-to-all framework which would fit absolute realism. (Elkana 1978, 309)

In chemistry one observes different relationships [rapports] between different bodies, which act such that they unite easily with one another. These relationships have their degrees and their laws. One observes their different insofar as, among several materials are confounded and that have some disposition to unite together, one perceives that one of these substances always unites constantly with a certain other [substance] preferably to all others.

Jean-Baptiste Lamarck (1744–1829) was a prolific writer, a multifaceted naturalist, and a zoologist by second profession. Throughout his adult life he lived up to his passion of politely contributing to the advancement of natural philosophy by publishing more than 30,000 pages, probably too much for even the most scrupulous (and persevering) historians of science who seek to reconstruct his theories and to shed some light on the role he played in late eighteenth-century and early nineteenth-century biology.

In his “A Programmatic Attempt at an Anthropology of Knowledge,” published in 1981, Yehuda Elkana briefly introduced the notions of dramatic and epic theater as metaphors for distinct and opposite conceptions of history. He elaborated more fully on this theme in a paper published in 1982 on the occasion of the Albert Einstein centenary celebration. Elkana there criticized the “myth of simplicity” surrounding Einstein, and proposed to replace a “facile holism” often attributed to Einstein with “two-tier thinking.” According to Elkana, Einstein's historical epistemology was a blend of an epic, contingent view of historical scientific change coupled with strong scientific realism.

Among those who know Yehuda's work, the term “two-tier thinking” is usually associated with a problematic relativist position (Elkana 1978). But “two-tier thinking” is not a name for a philosophical argument; it is best understood, I think, as a term designating certain conditions of knowledge: universal, or modern, or perhaps only postmodern conditions, but in any case, they are generalizations derived from anthropological and psychological observations on matters of facts. This is how things actually work in the sphere of knowledge: Western intellectuals and scientists tend to acknowledge that their truth claims and certainly their normative claims are incompatible with other claims that stem from other belief systems, frameworks of thought or genres of discourses, and there is no final, impartial instance of judgment to adjudicate between the incompatible claims and the conflicting systems. Lack of “final,” impartial judgment does not hinder people from taking their truth claims seriously and acting as realists within the world constituted by their particular belief systems — tier 1. But when they come to reflect upon it, as some of them do, sometimes, they acknowledge the context-dependence of this realism and the fact that there is no way to make good on its claim to universality; theirs, they know, is but one particular “belief system,” or “genre of discourse,” among many.

Although Cassirer's four-volume Das Erkenntnisproblem in der Philosophie und Wissenschaft der neueren Zeit has long been highly regarded as an example of historical scholarship — Cassirer was awarded the golden Kuno-Fischer Medal of the University of Heidelberg in July 1914 for the first two volumes (published 1906 and 1907) — its importance for understanding his theoretical position seems to have gone unrecognized. In the English-speaking world it is, unfortunately, only known through the fourth volume, and when this appeared in English in 1950 it met with a negative, even hostile, reception (see Passmore 1968, 315f.).

Modern thought would present only an incomplete and fragmentary picture of philosophy to us if we were to regard it as being completely disconnected from the elemental forces and sources of Greek philosophy. The corrective aspect that protects it from any such attempt at unmethodical isolation is, however, given within itself and in its own content. Its own inner progress necessarily leads it back to the principles and questions that distinguished Greek speculation, which it embodied in typical forms. The thought of the modern age proves its specificity in the fact that, notwithstanding the richness of content that it gains, it remains conscious of its relatedness to these basic logical forms and strives to return to them of its own accord. They will thus themselves appear to us of their own accord and incite us to regard their contents, if we just allow ourselves to follow the course of the investigation.