20 DISCOURSE ON THE STUDY 



that the words and signs used in our reasonings 

 are full and true representatives of the things sig- 

 nified; and, consequently, that when we use lan- 

 guage or signs in argument, we neither, by their 

 use, introduce extraneous notions, nor exclude any 

 part of the case before us from consideration. For 

 example : the words space, square, circle, a hundred, 

 &c., convey to the mind notions so complete in 

 themselves, and so distinct from every thing else, 

 that we are sure when we use them we know and 

 have in view the whole of our own meaning. It is 

 widely different with words expressing natural ob- 

 jects and mixed relations. Take, for instance, iron. 

 Different persons attach very different ideas to this 

 word. One who has never heard of magnetism has 

 a widely different notion of iron from one in the 

 contrary predicament. The vulgar, who regard this 

 metal as incombustible, and the chemist, who sees 

 it burn with the utmost fury, and who has other 

 reasons for regarding it as one of the most com- 

 bustible bodies in nature ; the poet, who uses it as 

 an emblem of rigidity ; and the smith and engineer, 

 in whose hands it is plastic, and moulded like wax 

 into every form ; the jailer, who prizes it as an 

 obstruction, and the electrician, who sees in it only a 

 channel of open communication by which that most 

 impassable of obstacles, the air, may be traversed 

 by his imprisoned fluid, have all different, and all 

 imperfect, notions of the same word. The meaning 

 of such a term is like a rainbow every body sees a 

 different one, and all maintain it to be the same. 

 So it is with nearly all our terms of sense. Some 

 are indefinite, as hard or soft, light or heavy (terms 



