330 THE POPULAR SCIENCE MONTHLY. 



pun, but one made unwittingly. Wliat is called tbe inelegance of 

 using the same word in one sentence, or in two consecutive sentences, 

 causes mental diplopia. For even if each of the two words has the 

 same dictionary meaning, we must bear in mind that a word loses 

 something of that kind of meaning when forming part of a propo- 

 sition, losing and taking meaning by and from its context. Hence the 

 second time the word comes there is a faint revival of the ideas it sym- 

 bolized when used the first time, along with a vivid revival of other 

 ideas it now symbolizes ; there is trivial confusion from slight mental 

 diplopia, like that from an ill-understood pun, I now give a more 

 striking example — one in which there is manifest diplopia without 

 confusion. 



A smell, say of roses, I now have makes me think of a room where 

 I passed much of my time when a child. Here clearly is " mental di- 

 plopia," and the mechanism of it is quite similar to that of the pun, 

 making allowance for caricature in the latter. For the true process is 

 that the smell of roses, now having, develops what we call the same 

 smell, but really another smell, that of roses once had, in the old room. 

 The two scents, linked together, bold together two dissimilar mental 

 states (1) present, now narrowed, surroundings, and (2) certain vague 

 quasi-former surroundings. When the scent of hay, or the caw of 

 rooks, rouses in us vague pleasurable feelings, the mechanism is of the 

 same kind, but the process is more complex. To further insist on the 

 fact that mentation is stereoscopic, with more or less manifest diplopia, 

 I give an example of mentation which is exceedingly common. While 

 Avriting I suddenly think of York Minster. Here is manifest mental 

 diplopia (1) narrowed consciousness of my present surroundings, with 

 (2) cropping-up of consciousness of some quasi-former surroundings. 

 Of course something, whether I can mentally seize it or not, in my 

 present surroundings, has developed a similar something associated 

 with York surroundings. 



Recapitulating, I can say that the process of all thought is double, 

 in degrees from a stereoscopic unity of subject and object to manifest 

 diplopia (two objective states for one subject). The process of all 

 thought is tracing relations of resemblance and difference, from sim- 

 plest perception — to say what a thing is, is to say what it is like and 

 unlike — up to most complex abstract reasoning. The formula of the 

 caricature of the normal process of thought is the " pretense" of some 

 resemblance between things vastly different — from punning, where the 

 pretended resemblances and real differences are of a simple order, up 

 to humor, where both are highly compound. We have the "play " of 

 mind in three degrees of evolution, three stages of increasingly com- 

 plex incongruousnesses. 



If I had time, I could, I think, show that this address on jokes is 

 not itself merely one big poor joke, but that what has been said applies 

 closely to the study of "mental symptoms" in serious diseases. I 



