2<5o ELEMENTS OF SCIENCE 



other of our higher faculties are our two powers of reason- 

 ing or inference. One of these is commonly termed induc- 

 tion, and it is the process by which we are enabled to form 

 judgments more or less probable, or even certain. Thus 

 when we have examined many kinds* of animals belonging 

 to one group, e.g., the group of opossums, and found 

 that they all possess certain peculiar bones, we judge that 

 if a new species is discovered it will also possess such 

 bones. Such a judgment, however, can rarely be an 

 absolutely certain one. But we may be certain in some 

 cases. Thus by the study of many kinds of rock, we may 

 recognise the truth, by means of fossils found in them, 

 that different animals have inhabited the earth at 

 different times. A farther development of this kind of 

 mental activity leads to a process which is most fruitful 

 in promoting scientific progress namely, the formation 

 and verification of hypotheses. This process consists of 

 guesses, based on a certain number of anterior observa- 

 tions, which guesses are subsequently tested by examining 

 whether certain facts, specially selected as tests, confirm 

 such guesses or not. 



The other process of reasoning is termed deduction or 

 ratiocination, and will be considered in the next chapter 

 wherein we shall introduce the student to the elements of 

 logic, and also make some additional remarks about 

 induction.* 



Amongst our many perceptions, one supremely im- 

 portant one is our perception whether or not anything 

 is true our perception of truth. The truth of every 

 proposition of every science with which we have so far 

 been concerned, consists in its conformity with fact. 

 " Truth " is a conformity of thought with things, and 



* See vost, p. 309. 



