nominalists during the middle ages could not have been more bitter than this Haeckel controversy threatens to become, and we need have no fear, so far as I can see, that the occupation with intellectual things is blunting the emotional side of the modern thinker's soul.
It is not my intention to join in the hue and cry against this man who has dared to offer the world a Weltanschauung, nor am I willing to stamp his work as unworthy of notice. It is true, Haeckel has provoked a fair share of the abuse that has been heaped upon him by his own intolerant attitude, but after all two wrongs do not make a right. I believe that it will be worth our while to hear patiently what Haeckel has to say, and then to subject his philosophy to the tests by which it will be judged at last when the discordant voices of the present are hushed and the author and his critics are sleeping in their quiet graves. A work that has made such an impression upon an age as the 'World Riddles' can not be ignored or thrown out of court without a hearing, and the hearing must be impartial and temperate, such a hearing as it is bound to receive at the bar of history. It expresses the views of large numbers of natural scientists to-day, although few would dare to make public confession of their faith, as the fearless Jena biologist has done; and as an expression of opinion coming from such a quarter, it deserves attention. I shall therefore try in what follows to give an exposition of Haeckel's thought, and to examine its value as a theory of the universe.
And first let us turn to our philosopher's theory of knowledge.[1] Our true knowledge, he says, is real in its nature; it consists of ideas (Vorstellungen) which correspond to really existing things. It is true we cannot know the innermost essence of this real world, of the thing in itself,[2] but we are convinced by impartial and critical observation and comparison that the external world makes the same impressions upon the sense-organs and brain of all normal rational individuals, and that the same ideas are formed by all persons whose organs of thought function normally. All our knowledge depends upon two physiological functions—upon sensation and upon the combination of the impressions thus gained, by association. The experiences which we receive from the external world through our sense-organs and sense-centers in the brain are transformed into ideas by other brain-centers, and these are combined into inferences by association. These inferences are both inductive and deductive, processes which have equal value. Other complicated brain operations, the formation of chains of reasoning, abstraction and conception, imagination, consciousness, thought and philosophy, are all functions of the ganglionic cells of the cerebral cortex.[3]
