Kierkegaard writes in his Journals: "What is the Absurd? It is, as may quite easily be seen, that I, a rational being, must act in a case where my reason, my powers of reflection, tell me: you can just as well do the one thing as the other, that is to say where my reason and reflection say: you cannot act and yet here is where I have to act".
Kierkegaard's concept of absurd is closely related to his concept of Paradox. The absurd is something or a state which cannot be rationally explained. It could be said that for Kierkegaard the absurd is any action which happens without a rational reason to justify it. Like the paradox, the absurd is linked to the collision between two opposing powers which in Kierkegaard's philosophy are the ethical and the religious, which prompts the "Leap of faith" from one to the other. The inability to mediate the two contradicting forces leaves the individual in a paradoxical state of absurd. In Fear and Trembling Kierkegaard gives the example of Abraham's absurd condition in which he faithfully intends to kill his own son Isaac while at the same time believing that God will keep him alive. This is for Kierkegaard the exemplary manifestation of the absurd faith.