PROPOSITIONS. 53 



very perception of an object involves its discrimination 

 from all other objects. But we may nevertheless be said 

 to detect resemblance as often as we detect difference. 

 We cannot, in fact, assert the existence of a difference, 

 without at the same time implying the existence of an 

 agreement. 



If I compare mercury, for instance, with other metals, 

 and decide that it is not solid, here is a difference between 

 mercury and solid things, expressed in a negative propo- 

 sition ; but there must be implied, at the same time, an 

 agreement between mercury and the other substances 

 which are not solid. As it is impossible in the alphabet 

 to separate the vowels from the consonants without at 

 the same time separating the consonants from the vowels, 

 so I cannot select as the object of thought solid things, 

 without thereby throwing together into another class all 

 things which are not solid. The very fact of not possess- 

 ing a quality, constitutes a new quality or circumstance 

 which may equally be the ground of judgment and classi- 

 fication. In this point of view, agreement and difference 

 are ever the two sides of the same act of intellect, and it 

 becomes equally possible to express the same judgment in 

 the one or other aspect. 



Between affirmation and negation there is accordingly 

 a perfect balance or equilibrium. Every affirmative propo- 

 sition implies a negative one, and vice versd. It is even 

 a matter of indifference, in a logical point of view, whether 

 a positive or negative term be used to denote a given 

 quality and the class of things possessing it. If the 

 ordinary state of man's body be called good health, then in 

 other circumstances he is said not to be in good health ; 

 but we might equally describe him in the latter state as 

 sickly, and in his normal condition he would be not sickly. 

 Animal and vegetable substances are now called organic, 

 so that the other substances, forming an immensely greater 



