Bertrand Russell on Dualism

“As regards knowledge of truths, there is a dualism. We may believe what is false as well as what is true. ...Since erroneous beliefs are often held just as strongly as true beliefs, it becomes a difficult question how they are to be distinguished from true beliefs. How are we to know, in a given case, that our belief is not erroneous? This is a question of the very greatest difficulty, to which no completely satisfactory answer is possible. There is, however, a preliminary question which is rather less difficult, and that is: What do we mean by truth and falsehood?”

“Death, says Socrates, is the separation of the soul from the body. Here we come upon Plato's dualism: between reality and appearance, ideas and sensible objects, reason and sense perception, soul and body. These pairs are connected: the first in each pair is superior to the second both in reality and in goodness. An ascetic morality was the natural consequence of this dualism. Christianity adopted this doctrine in part, but never wholly. There were two obstacles. The first was that the creation of the visible world, if Plato was right, must have been an evil deed, and therefore the Creator could not be good. The second was that orthodox Christianity could never bring itself to condemn marriage, though it held celibacy to be nobler. The Manichaeans were more consistent in both respects.”