For the first time, it was in Greek that reason was recognized as the only source of knowledge in contrast to mystical views. It was by Aristotle that this approach was highlighted. For this reason, we know Aristotle as an outstanding and an ultimate instance of Greek reason. In this article, based upon the early Christian theologian views, our hypothesis is that common sense, that we know as Greek reason, was the only source for knowledge. Accordingly, we have studied some of the great early Christian theologian views to find their concept of reason. Our conclusion is that when Christian theologians had characterized reason as worldly or human wisdom, they would have meant it the very Aristotelian-Greek concept, namely, the only source for common knowledge. In contrast, according to them, there was another source of knowledge, namely, “ faith” that was gained not by the reason but by the Grace.