Introduction
Humor and laughter make life more bearable, sometimes even enjoyable.
L. Weiss "Philosophie et vie" ( 1951)

Humor and the physiological response to it, laughter, are universal. As Rabelais is quoted in the article on French humor: "Laughter is what characterizes man." While laughter, the main response to humor, can be defined, measured and described, humor itself is an elusive concept. As with many psychological concepts, precise definitions are impossible. If you are asked to think about and name someone who has humor and someone who doesn't, you can do it easily. But when you try to define humor, it becomes much more difficult. For a scholarly example about the difficulties inherent in definitions, one can read the article in which Robert Miles tried to define the concept definition. He arrived at twelve perfectly valid definitions of the term ( 1957).

If concepts in humanities are not easy to define, theories proposing to explain them are even more difficult. However, this did not stop some of the most brilliant philosophers from proposing theories of humor. Their work is fascinating but never completely satisfying. George Mikes, the British humorist, expressed it rather nicely. Talking about philosophers' efforts to create theories, he wrote: "The philosopher is like a good athlete on the double bar; his movements are beautiful; his skill is breath--taking; his achievement admirable. But when he jumps off, he is where he was before he started: he had achieved nothing, he had progressed nowhere. . . . There is not one single statement--however simple, innocuous and self-evident--on which philosophers agree" ( Mikes, 1971, P. 19).

Theories on humor have a long history. Since Plato and Aristotle, philosophers such as Kant, Schopenhauer, and Hobbes, writers such as Baudelaire and George Eliot, and even humorists such as Leacock and Mikes have proposed theories to explain why people laugh. Diligent people have summarized and presented these theories in learned books ( Greig, 1923; Piddington, 1933; Bergler, 1956; Keith-Spiegel, 1972). There are more than a hundred such theories, some of course following the classic academic dictum on innovative research: "Give old phenomena new names." In full awareness of the danger, I shall nonetheless define humor, knowing perfectly well that not all will agree with the proposed definition. The definition is necessary in order to make the reader aware of what we, the writers of this book, mean by humor and the physiological phenomena most frequently accompanying it: laughter and smiling.

LAUGHTER, SMILING, AND HUMOR
Laughter is a daily phenomenon in humans, clearly visible and audible. It can be measured with great precision, and the best description of the physiological process of laughter was offered at the beginning of the century by Norbert Dearborn. He wrote:

There occur in laughter and more or less in smiling, clonic spasm of the diaphragm, in number ordinarily about eighteen perhaps, and contraction of most of the muscles of the face. The upper eyelid is elevated, as are also, to some extent, the brows, the skin over the glabella, and the upper lip, while the skin at the outer canthi of the eyes is characteristically puckered. The nostrils are moderately dilated and drawn upward, the tongue slightly extended, and the cheeks distended and drawn somewhat upward; in persons with the pinnal muscles largely developed, the pinnae tend to incline forwards. The lower jaw vibrates or is somewhat withdrawn (doubtless to afford all possible air to the distending lungs), and the head, in extreme laughter, is thrown backward; the trunk is straightened even to the beginning of bending backward, until (and this usually happens soon), fatigue-pain in the diaphragm and accessory abdominal muscles causes a marked proper flexion of the trunk for its relief. The whole arterial vascular system is dilated, with consequent blushing from the effect on the dermal capillaries of the face and neck, and at times the scalp and hands. From the same cause, in the main, the eyes often slightly bulge forwards and the lachrymal gland becomes active, ordinarily to a degree only to cause a "brightening" of the eyes, but often to such an extent that the tears overflow entirely their proper channels. ( Dearborn, 1900. p. 853)

Fortunately, we are not aware that our body goes through such changes during laughter. We are conscious of the pleasure produced by it and by the special meaning transmitted in the humorous message which made us laugh. While physiologically laughter is well understood, psychologically it is certainly more complex, since it can communicate many things. For instance, there is social laughter, with which we intend to signal to others that we understood and appreciated a joke. There is laughter of derision, victory, embarrassment, and even hysteria. From this, it should be clear that stimuli other than humor can produce laughter. Smiling can also be described from the physiological aspect. More than a century ago, Darwin wrote of the smile: By drawing backwards and upwards of the corners of the mouth, throu gh the contraction of the great zygomatic muscles, and by the raising of the upper lip, the cheeks are drawn upwards. Wrinkles are thus formed under the eyes, and, with old people, at the outer ends. . . . As in laughing and broadly smiling the cheeks and upper lip are much raised, the nose appears to be shortened, and the skin on the bridge becomes finely wrinkled in transverse lines, with other oblique longitudinal lines on the sides. The upper front teeth are commonly exposed. A well marked naso-labial ford is formed, which runs from the wing of each nostril to the corner of the mouth. ( Darwin, 1872, p. 210)

As with laughter, the psychological meanings of the smile can be numerous and varied. A welcoming smile, a smile of recognition, and an expression of embarrassment are just a few examples. Clearly, then, laughter and smiling are not exclusively responses to humor. However, they are the main reaction to it and thus can be used in a definition of humor. Humor is therefore defined as a social message intended to produce laughter or smiling. As with any social message, it fulfills certain functions, uses certain techniques, has a content, and is used in certain situations. These aspects of humor can be understood as relating to the questions of why people use humor (its functions), how it is transmitted (techniques), what it communicates (content), and where and when it is communicated (situation). Some of these aspects of humor are universal, characterizing humor everywhere. Others are more influenced by culture. At the present state of knowledge, theoretically one can see these aspects of humor on a continuum from universal to cultural. On this continuum techniques should be considered as most universal. There is no society in which humor has not been reported to exist. In all anthropological research in which cultures have een compared, the techniques of humor have been found to be the same...