KNOWLEDGE AND BELIEF. 307 



he attains to connected knowledge. But this know- 

 ledge remains defective and unsatisfactory until the 

 imagination supplements the inadequate power of 

 combination of the intelligence, and, by the associa- 

 tion of stored-up images, unites the isolated elements 

 into a connected whole. Thus are produced new 

 general presentative images, and these suffice to 

 interpret the facts preceived and satisfy " reason's 

 feeling of causality." 



The presentations which fill up the gaps in our 

 knowledge, or take its place, may be called, in a broad 

 sense, "faith." That is what happens continually in 

 daily life. When we are not sure about a thing we 

 say, I believe it. In this sense we are compelled to 

 make use of faith even in science itself; we conjecture 

 or assume that a certain relation exists between two 

 phenomena, though we do not know it for certain. If 

 it is a question of a cause, we form a hypothesis ; 

 though in science only such hypotheses are admitted 

 as lie within the sphere of human cognizance, and do 

 not contradict known facts. Such hypotheses are, for 

 instance — in physics the theory of the vibratory move- 

 ment of ether, in chemistry the hypothesis of atoms 

 and their affinity, in biology the theory of the molecular 

 structure of living protoplasm, and so forth. 



The explanation of a great number of connected 

 phenomena by the assumption of a common cause is 

 called a theoiy. Both in theory and hypothesis 

 " faith " (in the scientific sense) is indispensable ; for 

 here again it is the imagination that fills up the gaps 

 left by the intelligence in our knowledge of the con- 

 nection of things. A theory, therefore, must always 

 be regarded only as an approximation to the truth ; it 

 must be understood that it may be replaced in time by 



