THE PSYCHOLOGY OF JOKING. 329 



commonplace realism about simple things to be realism when applied 

 to very complex things. It seems at first glance more realistic to sup- 

 pose that sourness is inherent in vinegar than that it is always a sensa- 

 tion in some percipient. But that the former hypothesis is very un- 

 realistic is easily seen when we put such crude metaphysics in other 

 words ; the doctrine then is that part of the taster's own mind is out- 

 side himself. It is possible for the same person to be truly realistic in 

 simjile things, and to be intensely unrealistic in complex things. Thus, 

 the really practical man, who may tell us that he despises metaphysics, 

 may be crudely metaphysical when he deals with complex things — 

 "explaining," for example, that a man comatose does not move be- 

 cause he has lost consciousness. Surely the truly realistic conception 

 is that the comatose patient does not move any of his limbs from some 

 physical disability — for essentially the same reason that a hemiplegic 

 man does not move his arm and leg. 



I now go back to my small joke that punning is a slightly morbid 

 mental state, a ''mental diplopia," a caricature of the normal " diplopia" 

 of healthy mentation. From this point I make the assertion that the 

 " physiological insanity " of dreaming is diplopic — a caricature of that 

 of waking mentation. A physician reads in the day of the strained re- 

 lations of European states ; in his dream at night he is called in con- 

 sultation by Bismarck, and advises a course of the iodide of potassium 

 (directions for the application of the remedy were not given). Clearly, 

 there are here two very dissimilar mental states "pretending" to be 

 stereoscopic ; manifestly a seeming fusion of ideas of prescribing for a 

 patient with ideas of the attitude of European states. I hope some 

 time to be able to show that such diplopia has the same kind of mechan- 

 ism as that of the pun — that the two elaborate dissimilar states are held 

 together by two same, or similar, simple mental states. I go on to re- 

 mark that in some people there are beliefs as incongruously diplopic as 

 some states in dreams — diplopic in that way to other people, at any 

 rate : — (1). Killing a rabid dog to prevent people already bitten by it 

 going mad. (2), Imagining it to be possible to study what are called 

 " diseases of the mind " methodically without distinguishing between 

 the physical and the psychical. (3). A cleanly mother, from maternal 

 solicitude, refraining from washing the top of her baby's head, lest it 

 should come to have " water on the brain." (4). Imagining it to be 

 possible to investigate complex subjects without the use of hypotheses ; 

 for instance, that Harvey could have made observations and experi- 

 ments to j^rove the circulation of the blood without SKpjwsing before- 

 hand that it did circulate. (5). Anointing a blade with healing salve 

 to cure a wound inflicted by the blade. 



Once more I go back to punning for a new start, trying to show 

 again by very simple cases that punning is only a caricature of, and 

 therefore for the psychologist a valuable experiment on, the process of 

 normal mentation. I take first a case which is almost if not quite a 



