Ok, yes, the idea of using probabilities raises two issues -- knowing you have the right inputs, and having the right perspective. Knowing and valuing the proper inputs to most questions seems impossible because of the subjectivity of most issues -- while Bayesian judgements may still hold in the abstract, they are often not practical to use (or so I would argue).

Unreliable evidence, biased estimates etc. can, in fact, be taken into account.

Second, what do you think about the idea of "perspectivism" -- that there is only subjective truth in the world?

This.

You don't have to sign on completely to Nietzsche's theory to see its potential application, even if limited in scope. For example, a number of communication techniques employ a type of perspectivism because different people view issues through an "individual lens". In either case, seeing the world as constructed of shades of grey seems more practical and accurate relative to using probabilities. This seems at odds with Bayesian judgments that assume that probabilities yield one correct answer AND that a person can and should be able to derive that correct answer.

Throwing your hands in the air and saying "well we can never know for sure" is not as accurate as giving probabilities of various results. We can never know for sure which answer is right, but we can assign our probabilities so that, on average, we are always as confident as we should be. Of course, humans are ill-suited to this task, having a variety of suboptimal heuristics and downright biases, but they're all we have. And we can, in fact, assign the correct probabilities / choose the correct choice when we have the problem reduced to a mathematical model and apply the math without making mistakes.

The point i raise about communication techniques relates to your "offtopic" point. I assume you are a rationalist, and thus believe yourself to have superior decision making skills (at least relative to those that are not students (or masters) of rationality). If so, what is the value of your "off topic" point -- you clearly were able to answer my question despite its shortcomings -- why belittle someone that is trying to understand an article that is well-received by LW? Is the petty victory of pointing out my mistakes, from your perspective, the most rational way to answer my comment? I'm not insulted personally (this type of pettiness always makes me smile), but I'm interested in understanding the logic of your comments. From my perspective, rationality failed you in communicating in an effective way. It seems your arrogance could keep many from following and learning from LW -- unless of course the goal is to limit the ranks of those that employ rationality. What am I missing? (and the answer is no, i haven't considered using a spell or grammar checker other than the one provided by this site).

Oh, I'm not going to downvote your comments or anything. I just thought you might prefer your comments to be easier to read and avoid signalling ... well, disrespect, ignorance, crazy-ranting-on-the-internet-ness, and all the other low status and undesirable signals given off. Of course, I'm giving you the benefit of the doubt, but people are simply less likely to do so when you give off signals like that. This isn't necessarily irrational, since these signals are, indeed, correlated with trolls and idiots. Not perfectly, but enough to be worth avoiding (IMHO.)