sumption: Give me matter and I will build you a world. . . . But can he make the same boast with reference to the simplest plant or insect? Can he say: Give me matter and I will explain to you the evolution of a caterpillar?"
Each science endeavors to reduce the most diverse facts with which it deals to identity, to one underlying principle. Heat, light, sound, electricity are different forms of some underlying force or energy. Are states of consciousness referable to the same force, or must we assume another ultimate, of which both physical and mental facts are the expression, as the monists hold?
All these are problems that are worth considering. The difficulty of solving them and the disagreement existing between the attempts to solve them suggest another problem. The human mind has a tendency to unify, to reduce facts to ultimates, to first principles. What is the value of this tendency as a means of reaching truth? Can we know anything about these tilings? The instrument of knowledge, the human mind, without which there could be no science at all, is itself a fact which needs to be explained. We evidently employ the same methods in the different branches of knowledge, we explain facts by referring them to their antecedents, simply because this is the function of the mind. But is there no limit to this search for antecedents or causes? What epistemological value has the causal instinct? In fact, what does human knowledge consist in, and how is it possible, as Kant asks? Define its limits, before you set out on the vast sea of speculation. We need a science which will examine the nature and validity of knowledge, a theory of knowledge. As Helmholtz declares, no age can with impunity refuse the task of examining the sources of our knowledge and the ground of its validity. The different sciences employ the categories of thinking without investigating their validity. Philosophy must regard with suspicion everything that is not clear as day; it is 'nothing, if not critical.' In his attempt to explain the sensible world, the scientist often has recourse to the suprasensuous. Can we know anything of the suprasensuous or must we confine our efforts to the study of what our senses present to us? Must we accept DuBois-Reymond's verdict? "Concerning the riddles as to what matter and force are, and whether they can think, the natural scientist must once for all decide upon the verdict: Ignorabimus" Or shall we protest with Haeckel against the position that there can be invincible barriers to Natureikennen. There are many other problems which suggest themselves to an epistemology, or theory of knowledge.
Such a science not only forms the prelude to the most important part of philosophy, to metaphysics, but also assists the thinker in discover-
- DuBois-Reymond, Grenzen des Naturerkennens. Galileo made a similar statement.