2 Quotes by Frederick Charles Copleston

[O]ther thinkers have philosophised since the time of Plato, but that does not destroy the interest and beauty of his philosophy

Everyone who doubts knows that he is doubting, so that he is certain of this truth at least, namely the fact that he doubts. Thus every one who doubts whether there is such a thing as truth, knows at least one truth, so that his very capacity to doubt should convince him that there is such a thing as truth.