Freud developed detailed theories concerning the nature of humour and why some things are funnier than others. One way to put his theories in perspective is to look at tragic situations about which jokes have been created. Why would people make jokes about such events?

According to Freud, sexual and aggressive themes underlie much of what people consider humourous. Additionally, hostile humour is funnier when directed towards someone we dislike. Hostile humour can reduce tension, especially that caused by tragic or unnerving events.

Tendentious jokes - those about such things as hostility and sex - can provide insight into the unconscious of the joke teller as well as the respondent.

Aggressive jokes allow aggressive desires and feelings to be held in check, in a socially appropriate manner. These sorts of jokes are not only acceptable in society, but may even be encouraged. It's a great way to introduce uncomfortable topics in conversation, for instance. This is known as catharsis.

Thus, telling jokes about scary or sad events can be a way to reduce and relieve stress caused by the event.

Of course, jokes are funnier when directed towards someone we don't like. Studies show that men find humour about women funnier than that about men, and vice-versa.

An interesting note: it may seem that hostile humour told to an already hostile person may make things worse. Actually it reduces hostility in that person and is received better than by a relaxed person.

Tension is a big part of humour. The more tension involved, the funnier it is. Thus, more sensitive people are more likely to find something funnier than a calm, tensionless person. A person told a rat in a box might bite will find it funnier if it's actually a toy rat in a box than a person told the rat is harmless.

All in all, laughter serves an important psychological function, keeping us in a healthy mental state.