600 PSYCHOLOGY 



vincing, or at all events most plausible form. It would be an irre- 

 parable limitation if either of these methods did not apply in psych- 

 ology. In my opinion they not only do obtain, but must obtain. 

 The mental and the physical are so inextricably interfused that 

 quantitative and genetic uniformities could not exist in the physical 

 world if absent from consciousness. If our mental processes did not 

 vary in number, if they did not have time, intensity, and space 

 relations, we should never have come to apply these categories in 

 physics, chemistry, or astronomy. I am not prepared to attempt to 

 clear up the logical questions involved; when water is muddy it is 

 often wise to wait for it to settle rather than to keep stirring it up. 



Under the conditions of modern science nearly all observations 

 are experiments, and nearly all experiments are measurements. A 

 sharp distinction is usually drawn between an experiment and an 

 observation. Thus Wundt, following Mill and other logicians, 

 defines an experiment as an observation connected with an inten- 

 tional interference on the part of the observer in the rise and course 

 of the phenomena observed. But it is as properly an experiment 

 to alter the conditions of observation as to alter the course of the 

 phenomena observed. If the astronomer goes to the ends of the 

 earth and photographs a solar eclipse, making all sorts of measure- 

 ments and calculations, we may say that this is an observation and 

 not an experiment, but we have not made a useful definition; neither 

 do we gain anything by deciding whether it is an experiment when 

 a baby pulls apart a doll to see what is inside. The real distinction 

 is between the casual experimenting and observing of daily life, and 

 the planned and purposive experiment and observation of science. 

 Science is experimental qua science. 



I consequently object to making experimental psychology a 

 branch of psychology. It is a method in psychology, which is ex- 

 tended just as rapidly as psychology becomes a science. The purely 

 introspective or analytic observer does, according to the current 

 definition, continually make experiments, because his introspection 

 itself alters the process that he is observing, thus sometimes making 

 his observations invalid as a description of natural conditions. On 

 the other hand, the student in the laboratory may measure the pro- 

 cess without any introspection or interference with it, and this may 

 not be technically an experiment at all, but it gives a scientific 

 description of the normal course of mental life. We are told that 

 Adam gave a very appropriate name to the hog; science is not 

 always so fortunate in its nomenclature. 



Most experiments, letting experiments mean attempts to increase 

 scientific knowledge, are also measurements. Measurement is only 

 a description; but it has proved itself to be the most economical, 

 wide-reaching, and useful form of description. What language was 



