After reading each philosopher's personal definition of humor, it seems that Kierkegaard's view of humor in some way encompasses the viewpoints of the other three philosophers. Kant's Philosophy of Laughter talks about the physical side of humor, stating that the pleasure we derive from a comical story comes from our gut rather than our mind. For him, the foundation of humor is contradiction. We only laugh, or smile wrily, at a story that ends in a way we did not expect. To this end, humorous stories do not follow a predictable path from beginning to end, but are rather characterized by chance and inconsistency. Kant also mentions that a lot of humor is built around the consequences of naivete. We laugh at the actions of a naive person, but only, Kant states, in a compassionat, "good-hearted" kind of way.
On the opposite end of the spectrum, Plato's view of humor is much less sympathetic. He states that the only object of humor is human folly or vice. Because of this, humor is based solely on malice, something that "causes the soul pain". He believes that humor is a mixture of pleasure and pain, as well as something that promotes lack of self-control. Because of this, he says that it must be avoided at all costs.
Hobbes shares a somewhat similar view of humor, stating that it is simply an expression of vainglory. Its object is the misfortune of others - both our friends and our enemies - and laughter stems from the sudden feeling of exaltation and superiority that accompanies witnessing someone else's misfortune. He supports this view of humor by saying that we never laugh at jokes made at our own expense, only those directed at the expense of others.
Kierkegaard brings elements of these three theories into his own view of humor. Like Kant, he aserts that the comical is based primarily on contradiction. Like Plato and Hobbes, Kierkegaard believes that a lot of humor is based upon the misfortunate situation of others. However, he continues to say that the misfortune alone does not determine if a story is comical. Rather a story based on misfortune is only funny if the object of misfortune is aware of a clear path out of his misfortune. Without this option, a story of misfortune is simply tragic and not comical. Kierkegaard's definition of humor is much more detailed and complex than those of the other three because he also brings in the situational aspect of humor, describes different levels of humor, and condemns Plato's belief that life should be devoid of everything comical. Because of this, Kierkegaard's theory seems to be the most applicable to humor in the modern world.