xxxiil.] MENTAL DEVELOPMENT. 73 



1 hear the twofold note of a cuckoo, its two notes are an 



instance of the succession of two sensations in time. If I 



see the cuckoo while I hear it, the sound and the sight are 



two sensations co-existent in time. For brevity, let us call 



this the relation of succession. Succes- 



sion. 

 3. The relation of co-existence or separation in space. 



If I feel two objects, one with each hand, this is a case of 

 the sepmrition of two sensations in space. If I press one 

 hand on a slab of marble, and find it both cold and hard, 

 this is a case of the co-existence of two sensations in space. 

 For brevity, let us call this the space-relation. Space- 



Likeness, succession, and the space-relation are, I believe, 

 the only simple and elementary relations that are possible 

 between sensations. But I believe there is a fourth relation 

 between feelings which is also a perfectly simple one ; 

 namely, that of cause and effect. This relation cannot 

 exist between two feelings of mere sensation; one im- 

 pression of sensation cannot cause another. But an 

 impression of sensation may cause an emotion, as when 

 the sight of food causes a desire to eat it ; and one action 

 of mind in emotion, thought, or will, may be the cause 

 of another. For brevity, let us caU this the relation of 



causation. Causatiou. 



All these four kinds of relation are, I believe, directly 

 cognised by the mind ; and these cognitions constitute the 

 ground of thought. It is not, I believe, disputed by any 

 that the cognition of simple relations is the ground and the 

 germ of thought ; but it is under discussion what relations 

 are really simple, primary, and incapable of being resolved 

 into others. JVIill and Bain regard the relations of likeness 

 and of succession as the only ones which are really 

 simple ; the space-relation and causation are, according 

 to them, ultimately resolvable into the relation of suc- 

 cession. In the following chapters I shall have to state 

 my reasons for differing from them ; but in this I prefer 

 only to state my belief as to what the primary relations 

 are, and to go on with the subject of the development 

 of the power of thought out of the cognition of simple 

 relations. 



