Why do we laugh?

In our world, laughter is second nature.  However, from a psychological standpoint, the phenomenon is deceivingly complicated.  Even before the foundation of modern psychology, several experts have attempted to find a simple explanation for its existence in everyday life.  The famous 18^th century philosopher, Immanuel Kant, stated that laughter is merely a sudden relief of tension.  More recently, Sigmund Freud made the claim that it functions as a method of releasing aggression and libido in a socially acceptable way.   In today’s psychological world, there are a few new ideas on laughter.  Featured in Psychology Today is Alastair Clarke’s published theory of laughter and its relationship to the brain’s ability to recognize normal cognitive patterns.

According to Clarke, what makes something funny or laughable is the element of surprise that is associated with it.  For example, a joke is only usually effective if the punch line is unpredictable.  When the person knows the punch line, whether they figure it out or have heard the joke before, laughter hardly ever follows.  This makes sense in terms of uncomfortable laughter as well.  If a situation makes an individual uneasy, some will let out a laugh.  The feelings associated with this reaction come from a break from the normal mental state.  Whether a clever quip or a quick sensation of being uncomfortable, the mind recognizes a deviation from what is expected and lets out the response of amusement.

http://www.psychologytoday.com/blog/the-playing-field/200806/why-we-laugh