492 PSYCHOLOGY. 



the mind-stuff theory in psychology regard as their ideal. 

 So that, following the analogy of our instances, one might 

 easily be tempted to generalize and to say that all difference 

 is but addition and subtraction, and that what we called 

 ' differential ' discrimination is only 'existential ' discrimina- 

 tion in disguise ; that is to say, that where A and B differ, 

 we merely discern something in the one which the other is 

 without. Absolute identity in things up to a certain -point, 

 then absolute non-identity, would on this theory take the 

 place of those ultimate qualitative unlikenesses between 

 them, in which we naturally believe ; and the mental func- 

 tion of discrimination, ceasing to be regarded as an ultimate 

 one, would resolve itself into mere logical affirmation and 

 negation, or perception that a feature found in one thing, 

 in another does not exist. 



Theoretically, however, this theory is full of difficulty. 

 If all the differences which we feel were in one direction, 

 so that all objects could be arranged in one series (how- 

 ever long), it might still work. But when we consider the 

 notorious fact that objects differ from each other in divergent 

 directions, it grows well nigh impossible to make it do so. 

 For then, supposing that an object differed from things in 

 one direction by the increment d, it would have to differ 

 from things in another direction by a different sort of incre- 

 ment, call it d'; so that, after getting rid of qualitative un- 

 likeness between objects, we should have it back on our 

 hands again between their increments. We may of course 

 re-apply our method, and say that the difference between 

 d and d' is not a qualitative uulikeness, but a fact of com- 

 position, one of them being the same as the other jAus an 

 increment of still higher order, 6 for example, added. But 

 when we recollect that everything in the world can be com- 

 pared with everything else, and that the number of direc- 

 tions of difference is indefinitely great, then we see that the 

 complication of self-compoundings of the ultimate differen- 

 tial increment by which, on this theory, all the innumerable 

 unlikenesses of the world are explained, in order to avoid 

 writing any of them down as ultimate differences of kind, 

 would beggar all conception. It is the mind-dust theory- 



