I want to say that there are two ways by which we determine that x is true. The first, and least often followed, is logic: the truth emerges as a conclusion to an inevitable logical sequence. Scientific knowledge, when it is itself, is of this form as much as philosophy is. The other is what T.S. Eliot refers to when he says, "We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time." It is the knowledge of feeling at home. It's full of dangers and misinterpretations. But it is essential.