Introductory. 25 



related to the same sector of a circle, or tries to use 

 the formula of one for that of the other, will waste 

 his own labors and mislead all who trust in him. 

 There is one part of the quadrant in which the 

 tangent equals the sine of ninety degrees, and the 

 formula of one might be used for that of the other 

 without essential error. But after passing that 

 point they differ more and more in value, until at 

 another part of the quadrant no number is suffi- 

 ciently great to express the difference between 

 them. The change in the comparative value of 

 these two elements is analogous to the divergence 

 between the different elements in man's nature, 

 that may, under certain conditions, be expressed by 

 the same formulas, but which demand for their 

 full treatment modes of thought and formulas of 

 language widely different from each other. 



As I propose to lecture on Instinct it might fair 

 ly be claimed that I should define the word at the 

 outset. If I were to do so, few of my audience 

 would agree with me fully. We should not agree 

 where Instinct begins to control action nor where it 

 gives place to another guide. It^ nature and office 

 would both be subjects of controversy. Were I to 

 copy the best definitions ever written there is not 

 one of them that some of us would not consider de- 

 fective in some respects. It would either take for 

 granted what we should not accept or it would deny 

 directly or by implication what we are ready to as- 

 sume as true. But we may be guided by these def- 

 initions, provisionally, treating them like bills before 

 2 



