COMMON SENSE (aND SCIENCE ) 13 



the child's formation of concepts. Piaget emphasizes the importance 

 of concepts of "conservation" in the elaboration of the child's vision 

 of the world. Only by way of his growing recognition of invariants, 

 and invariance, does he come at last to find his world intelligible. 

 Lorenz identifies the essence of Gestalt perception as 



. . . the single function of extricating the essential constant factor 

 by abstracting from the inessential variable sensory data. The differ- 

 entiation of this function attains an amazing development in the serv- 

 ice of shape constancy and it needs only to be driven one little step 

 further to make possible an absolutely new operation miraculously 

 analogous to the formation of abstract, generic concepts. 



Whether or not one accepts the Gestalt theory of "extrication," of 

 the constant factor, one recognizes how very natural will be the 

 emergence and refinement of functional capacity for this discrimina- 

 tion in creatures evolved under the pressure of natural selection. The 

 immense value of that "one little step further" is amply suggested by 

 Bartlett's analysis of the choice and arrangement of evidence by nor- 

 mal subjects placed in problem-solving situations. He strongly em- 

 phasizes the leading part played 



... by the detection of points of agreement. It is well known that 

 points of agreement are inherently less easy to detect than points of 

 difference. Perhaps the most important distinction between the two, 

 from our present viewpoint, is that the detection of differences alone 

 leads nowhere in particular in a positive sense, but the detection of 

 agreement may. Thus, if one instance is observed to differ in some 

 way from another, it may perhaps be said that something already 

 established about the one is not applicable to the other; but if two 

 instances are observed to agree in some way, it may possibly be im- 

 plied that something already established about the one is applicable 

 to the other. It seems fairly certain that, in a cognitive sense, all ad- 

 vance of knowledge comes by using agreements to get a move on, so 

 to speak, and then using differences to keep the move within limits, 

 and to show where a new direction of move becomes necessary. 



The normative factors. In Lorenz' view, the constant factor in ex- 

 perience is not so much "given to " as "computed by" the organism. 

 In some degree each must create concepts for himself— and this may 

 seem to raise a serious problem. How can we all come, as we do, to 

 a common understanding of the concepts of common sense? Norma- 

 tive influences plainly are at work. 



