What is seen by a natural light cannot be denied, but a mere inclination may be towards what is false.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“, and it therefore seems reasonable to suppose that a foreign thing imprints its likeness on me. But are these good reasons? When I speak of being “taught by nature” in this connection, I only mean that I have a certain inclination to believe it, not that I see it by a natural light. What is seen by a natural light cannot be denied, but a mere inclination may be towards what is false. And as for ideas of sense being involuntary, that is no argument, for dreams are involuntary although they come from within. The reasons for supposing that ideas of sense come from without are therefore inconclusive.” source