 Ross might say in reply in the case of right opinion you cannot rule out that such causes are operating on your opinion, whereas in the case of knowledge you can, because, on his conception of knowledge, when you know, you know you know. You have complete conviction (RG 147). This might make knowledge more valuable. And, he might continue, even if you can rule out such causes in the case of right opinion right opinion is less valuable than knowledge because it is in some way always based on conjecture and merely contingent connections between ideas and so held with some degree of diffidence.