1 68 THE GRAMMAR OF SCIENCE 



in each depends upon the degree of our examination and 

 observation. To a casual observer all the sheep in a 

 llock appear the same, but the shepherd individualises 

 each. Two coins from one die, or two engravings from 

 one block, will always be found to possess some distin- 

 guishing marks. We may safely assert that absolute 

 sameness has never occurred in our experience. No 

 "permanent" group of sense-impressions or "object" 

 even is exactly the same at two different times. Various 

 elements in the group have changed slightly with the 

 time, the light, or the observer. Take a polished piece of 

 metal and note two parts of its surface ; they appear 

 exactly alike, but the microscope reveals their want of 

 sameness. Thus sameness is never a real limit to our 

 experience of phenomena ; the more closely we examine, 

 the less is the sameness. Yet, as a conception, the same- 

 ness of two groups of sense-impressions is a very valid 

 idea, and the basis of much of our scientific classification. 

 In the sphere of perceptions sameness denotes the identity 

 for certain practical purposes of two slightly different 

 groups of sense-impressions. In the sphere of conceptions, 

 however, sameness denotes absolute identity of all the 

 members of either group ; it is a limit to a process of 

 comparison which cannot be reached in the perceptual 

 world. 



The idea of continuity, in the sense in which we are 

 now considering the word, involves that of sameness. If 

 I take a vessel of water, I find a certain permanent group 

 of sense-impressions which leads me to term the contents 

 of the vessel \\ater ; if I take a small quantity of the 

 water out of the vessel I find the " same " group, and this 

 still remains true if I take a smaller and smaller quantity, 

 even to a drop. I may continue to divide the drop, but 

 apparently as long as the portion taken remains sensible 

 at all, there is the same group of sense-impressions, and I 

 term the fraction of the drop water. Now the question 

 arises, if this division could be carried on indefinitely 

 should we at last reach a limit at which the group of 

 sense-impressions would change not only quantitatively, 



