VERIFICATORY TECHNIQUES 229 



roneously drawn from the hypothesis. The amateur detec- 

 tive often finds to his dismay that the concept "murderer" 

 does not strictly imply the many things which he sup- 

 posed it to imply, and consequently that the one who ac- 

 cording to his reckoning could not have committed the 

 murder is the one who really did. Even empirical generaliza- 

 tions are subject to exception, and these generalizations 

 which are founded on the imaginative anticipation of what 

 would occur from a state of affairs nowhere realized cannot 

 be expected to have a high degree of necessity. Hence it is 

 always advisable to reconsider the implicative relation before 

 rejecting the hypothesis. 



In the third place, infirmation may be due to the failure 

 to exert proper control either over the experimental or over 

 the observational set-up. All verification, as was pointed 

 out earlier in the chapter, involves noting what happens 

 when certain conditions, partly in the observer, and partly 

 in the physical medium, are established. That sodium burns 

 with a yellow flame can be confirmed if the observer places 

 his body and mind in a certain state of readiness, and if he 

 places a piece of sodium in the physical situation which 

 will produce the burning. But through inadvertence the 

 observer may fail to realize one or more of these conditions; 

 he may fail to look when the flame occurs, or he may not 

 be attending to the event and thus he may fail to see it, 

 or he may not have been sufficiently careful in setting up 

 the physical situation. Under any of these conditions the 

 predicted yellow flame may fail to occur for the awareness 

 of the observer. Examination of these conditions should 

 therefore be made before the hypothesis is rejected. Such 

 examination involves, on the part of the observer, the as- 

 certainment of whether normal conditions of observation 

 prevail; the establishment of normal conditions in the case 

 of the movement of verification is more difficult than in the 

 case of the movement of discovery, for preconceived ideas 

 are important sources of error; the observer is prone to 

 read into the situation that which he expects to occur. But 



