Laughter, as the cliche has it, is 'liberating', i.e. tension-relieving. Relief from stress is always pleasurable, regardless whether it was caused by hunger, sex, anger, or anxiety. Under ordinary circumstances such relief is obtained by some purposeful activity which is appropriate to the nature of the tension. When we laugh, however, the pleasurable relief does not derive from a consummatory act which satisfies some specific need. On the contrary: laughter prevents the satisfaction of biological drives, it makes a man equally incapable of killing or copulating; it deflates anger, apprehension, and pride. The tension is not consummated—it is frittered away in an apparently purposeless reflex, in facial grimaces, accompanied by over-exertion of the breathing mechanism and aimless gestures. To put it the other way round: the sole function of this luxury reflex seems to be the disposal of excitations which have become redundant, which cannot be consummated in any purposeful manner.Koestler tries to find support for his theory of laughter by looking at what some of the major philosophers of the past have said on this subject. Here's another excerpt from the chapter:
Among the theories of laughter that have been proposed since the days of Aristotle, the 'theory of degradation' appears as the most persistent. For Aristotle himself laughter was closely related to ugliness and debasement; for Cicero 'the province of the ridiculous ... lies in a certain baseness and deformity'; for Descartes laughter is a manifestation of joy 'mixed with surprise or hate or sometimes with both'; in Francis Bacon's list of laughable objects, the first place is taken by 'deformity'. The essence of the 'theory of degradation' is defined in Hobbes's Leviathan:
The passion of laughter is nothing else but sudden glory arising from a sudden conception of some eminency in ourselves by comparison with the infirmity of others, or with our own formerly.
Bain, one of the founders of modern psychology, followed on the whole the same theory: 'Not in physical effects alone, but in everything where a man can achieve a stroke of superiority, in surpassing or discomforting a rival, is the disposition of laughter apparent.’
For Bergson laughter is the corrective punishment inflicted by society upon the unsocial individual: 'In laughter we always find an unavowed intention to humiliate and consequently to correct our neighbor.' Max Beerbohm found 'two elements in the public's humor: delight in suffering, contempt for the unfamiliar'. McDougall believed that 'laughter has been evolved in the human race as an antidote to sympathy, a protective reaction shielding us from the depressive influence of the shortcomings of our fellow men.'This is a pessimistic view of laughter—the view that laughter is not a sign of some kind of supreme joy, but a way of releasing the suppressed feelings of derision, contempt and hatred. But it can't be denied that people often break into laughter at the sight of things that are clownish and degraded.