INTRODUCTORY EXPLANATIONS. 



pen. If I ask, again, which is most probable, that his 

 ship will arrive, or that he will, if he draw, draw either 



o, or 6, or c, or x, or y, or z, he will answer, the 



second, for it is quite certain. Now suppose I write the 

 following series of assertions : 



He will draw no letter (a drawing supposed). 



He will draw a. 



He will draw either a or b. 



He will draw either a, or 6, or c. 



He will draw either a or b or or y. 



He will draw either a or b or or y or %. 



and making him observe that there are, of their kind? 

 propositions of all degrees of probability, from that which 

 cannot be, to that which must be, I ask him to put the 

 assertion that his ship will arrive, in its proper place 

 among them. This he will perhaps not be able to do, 

 not because he feels that there is no proper place, but 

 because he does not know how to estimate the force of his 

 impressions in ordinary cases. If the voyage were from 

 London Bridge to Gravesend, he would (no steamers 

 being supposed) place it between the last and last but 

 one : if it were a trial of the north-west passage, he 

 would place it much nearer the beginning ; but he would 

 find difficulty in assigning, within a place or two, where 

 it should be. All this time he is attempting to compare 

 the magnitude of two very different kinds (as to the 

 sources whence they come) of assent or dissent ; and he 

 shows by the attempt that he believes them to be of the 

 same sort. He would never try to place the weight of 

 his ship in its proper position in a table of times of high 

 water* 



We also see, secondly, that the impression called cer- 

 tainty is of the character of a very high degree of 

 probability. Out of 1,000,000 of children born, it is 

 certain some will die aged 50. But by gradual pro- 

 gression, our unassisted judgment makes us believe 

 that we may correctly say that it is 1,000,000 times as 

 B 3 



