The title of this essay is meant to be rather startling, and more startling than the phrase "Christian philosophy" which provoked no little controversy some few years ago. That phrase was introduced by the medievalist Etienne Gilson to describe the contributions to philosophy of such thinkers as St. Thomas Aquinas and St. Bonaventure. Gilson conceded to opponents that there could no more be a Christian philosophy, in the strict sense of the term, than a Christian mathematics or a Christian physics. All these studies were, in their formal idea, unconnected with matters of religious belief. But he insisted that as a matter of concrete historical fact the lived Christianity of certain medieval figures had led them to philosophical developments and discoveries that would not have been developed or discovered otherwise. In this sense, he declared, there could be Christian philosophies. It is not my intention to enter again on this controversy here. I draw attention to it merely to show how different my own topic of discussion is from Gilson's. Gilson was concerned with the question whether there can be a philosophy that is Christian. I am concerned with the question whether there can be a philosophy that is not Christian.
Now this may seem a wholly bizarre question and one that it is easy to answer. For surely not only was Gilson right that philosophy is different from religion in its very idea, but also as a matter of historical fact there are many philosophies in the world that are not at all Christian. One thinks immediately of those of ancient Greece, China, and India, of those of the medieval Jewish and Islamic worlds, and of most of the philosophies of the modern day too. Well, perhaps. But I think my thesis, with a few qualifications, can be made to stand.
When philosophy is said to differ in its formal idea from religion, especially a professedly revealed religion like Christianity, what is typically meant is that philosophy is the study of things as they can be known by the light of unaided reason while religion, or, more precisely, theology, is the study of things as they can be known by the light of supernatural revelation. Clearly, if this is the way philosophy and religion are being understood then there is and can be no formal overlap between the two studies. There can, at most, be the sort of historical overlap in the concrete existence of individual thinkers that Gilson mentions and argues for. I want, however, to question this way of understanding philosophy or this way of defining its essential idea. For that definition is not and never was the definition of philosophy as that term was typically understood, at least up until the modern period.
Let me begin with the second-century Christian saint, Justin Martyr. Gilson appealed to Justin Martyr in his own discussion, but failed, in my view, to take Justin's views seriously enough. Gilson, along with all the others involved in the controversy over Christian philosophy, was too wedded to the formal definition just mentioned to see that it did not apply in the case of Justin. Gilson recalls, for instance, how Justin went about from one professed philosopher to another in search of God and wisdom until he found an old man who instructed him in the teaching of the prophets and the Gospels. Justin came to the conclusion that this was the only sure and profitable philosophy and he describes his conversion to Christianity as his becoming a philosopher.
It is evident from this, and from other texts, that Justin was not using the word "philosophy" in a way that distinguished it from the Christian faith. On the contrary, the Christian faith for him was the true and complete philosophy. It was what he had been looking for all along, and indeed what all philosophers had been looking for all along, namely the sure and true path of wisdom. Refusing to become a Christian was, for Justin, the same as refusing to remain a philosopher, and …