As a philosopher, Kierkegaard is often either hailed or condemned for opposing reason to personal religious Christian faith and is probably most renowned for his declaration that 'faith begins where thought leaves off'; but Kierkegaard, as a man of intelligence, has to begin with and take on thought, in particular the thought that thinks that one can know that God exists, whether one is a religious believer or not. For Kierkegaard, therefore, the very thinking through of the philosophical implica­tions of his own personal religious faith and of those who argue for the knowability of the existence of God are inextricably linked and integral to his conception of philosophy as rigorous unscientific religious thought. For his critics, such as Hei­degger, and many like him, one can be either a thinker or a religious believer; but Kierkegaard is, par excellence, a religious thinker. This paper, therefore, examines Kierkegaard's religious thinking on its own terms, that is to say, as taking on and dealing with arguments for the existence of God which he found, before and after Kant, in the tradition of philosophical thinking, and which required him to develop new lines of thinking in philosophy in general and in post-Kantian philosophy of religion in particular.