I. Haeckel and His Opponents

Besides those opponents of monism who are of opinion that the contemplation of the phenomena of the world leads up to spiritual beings, who are independent of material phenomena, there are still others[^10] who seek to save the domain of a supernatural order hovering over the natural one, by denying entirely to man's power of knowing the capacity to understand the ultimate grounds of the world-happenings.[^11] The ideas of these opponents have found their most eloquent spokesman in Du Bois-Reymond. His famous “Ignorabimus” speech, delivered at the Forty-fifth Congress of German Scientists and Doctors (1872), is the expression of their confession of faith. In this address Du Bois-Reymond describes as the highest goal of the scientist the explanation of all world-happenings, therefore also of human thinking and feeling, by mechanical processes. If some day we shall succeed in saying how the parts of our brain lie and move when we have a definite thought or feeling, then the goal of natural explanation will have been reached. We can get no further. But, in Du Bois-Reymond's view, we have not therewith understood in what the nature of our spirit consists. “It seems, indeed, on superficial examination, as though, through the knowledge of the material processes in the brain, certain mental processes and dispositions might become intelligible. Among such I reckon memory, the flow and association of ideas, the consequences of practice, the specific talents, and so on. A minimum of reflection, however, shows that this is a delusion. Only with regard to certain inner conditions of the mental life, which are somehow of like significance with the outer ones through sense impressions, shall we thus be instructed, not with regard to the coming about of the mental life through these conditions.