At this point it might be necessary to clarify that I make a distinction between knowledge and opinion. I subscribe to the standard definition of knowledge as justified true belief (JTB). As Bret Watson explains, JTB consists of:

First, belief: you do not know something unless you also hold it as true in your mind; if you do not believe it, then you do not know it. Second, truth: there can be no knowledge of false propositions; belief in a falsehood is delusion or misapprehension, not knowledge. Third, justification: the belief must be appropriately supported; there must be sufficient evidence for the belief.

Opinion, in my view, differs from knowledge in that in that it is a true belief that either cannot or has not been adequately justified (and is also not, like knowledge of God, a properly basic belief). The support for the opinion is based on subjective probability (i.e., dependent on the person making the assessment) rather than objective probability (e.g., a probability, like the outcome of a die roll, that everyone agrees on).

Not all subjective probabilities, of course, are equally probable. If you possess relevant information that I do not have, then your opinion may be more likely to be true than mine. (It could also be the case that you possess actual knowledge - a justified true belief - while I only have an opinion - a subjectively probabilistic true belief.) What if neither of us, though, harbors relevant information? How do we judge between two opinions when each are based on a subjective probability? And how do we know how much confidence we should have in our opinions?

The Italian statistician Bruno De Finetti offered one method to help determine the true subjective probability of an event that is useful for this task. The De Finetti Game is a method to gauge someone's confidence in the chances of a given event occurring by measuring it against a lottery with a known probability.

Say for example a friend claims he is 95% sure he aced a test. Is he really that confident? Offer him a hypothetical choice. He can either get the result of the test, and if he aced it, he wins one million dollars, or he can randomly select a ball from a bag. There are 90 red balls and 10 blue in the bag, and if he picks a red ball then he wins the million. Now if he doesn't choose his test score then he is at most 90% confident.

Now tell him that there are now 70 red balls in the bag and 30 black ones. If he answers that he would rather wait on the results of the test rather than draw, then he is between 70-90% sure of the outcome. You can keep adjusting the ratio of red to blue balls until he chooses the test score to find out how confident he really is. The final outcome is the person's true subjective probability.

The true subjective probability behind all of my opinions ranges from 51% to 99%. (If it fell below 51% I would have no reason to maintain that opinion rather than accept its alternative.) Unless I can muster enough warrant to move an opinion into the knowledge category, I have to acknowledge that there is a statistical likelihood -- whether trivial or significant -- that I could be wrong. No matter how confident I may appear in expressing my opinion, I am almost always aware that I could be in error. This is what I refer to as "humble certitude." I believe this is the proper attitude to maintain about opinions and that if provides a sufficient hedge against false pride.

Of course, that's just my opinion. I could be wrong.