assigning numerical probabilities to common-sense conclusions and beliefs is meaningless
It is risky to deprecate something as "meaningless" - a ritual, a practice, a word, an idiom. Risky because the actual meaning may be something very different than you imagine. That seems to be the case here with attaching numbers to subjective probabilities.
The meaning of attaching a number to something lies in how that number may be used to generate a second number that can then be attached to something else. There is no point in providing a number to associate with the variable 'm' (i.e. that number is meaningless) unless you simultaneously provide a number to associate with the variable 'f' and then plug both into "f=ma" to generate a third number to associate with the variable 'a', an number which you can test empirically.
Similarly, a single isolated subjective probability estimate may seem somewhat meaningless in isolation, but if you place it into a context with enough related subjective probability estimates and empirically measured frequencies, then all those probabilities and frequencies can be combined and compared using the standard formulas of Bayesian probability:
So, if you want to deprecate as "meaningless" my estimate that the Democrats have a 40% chance to maintain their House majority in the next election, go ahead. But you cannot then also deprecate my estimate that the Republicans have a 70% of reaching a House majority. Because the conjunction of those two probability estimates is not meaningless. It is quite respectably false.
I think you're not drawing a clear enough distinction between two different things, namely the mathematical relationships between numbers, and the correspondence between numbers and reality.
If you ask an astronomer what is the mass of some asteroid, he will presumably give you a number with a few significant digits and and uncertainty interval. If you ask him to justify this number, he will be able to point to some observations that are incompatible with the assumption that the mass is outside this interval, which follows from a mathematical argument base...
Please read the post before voting on the comments, as this is a game where voting works differently.
Warning: the comments section of this post will look odd. The most reasonable comments will have lots of negative karma. Do not be alarmed, it's all part of the plan. In order to participate in this game you should disable any viewing threshold for negatively voted comments.
Here's an irrationalist game meant to quickly collect a pool of controversial ideas for people to debate and assess. It kinda relies on people being honest and not being nitpickers, but it might be fun.
Write a comment reply to this post describing a belief you think has a reasonable chance of being true relative to the the beliefs of other Less Wrong folk. Jot down a proposition and a rough probability estimate or qualitative description, like 'fairly confident'.
Example (not my true belief): "The U.S. government was directly responsible for financing the September 11th terrorist attacks. Very confident. (~95%)."
If you post a belief, you have to vote on the beliefs of all other comments. Voting works like this: if you basically agree with the comment, vote the comment down. If you basically disagree with the comment, vote the comment up. What 'basically' means here is intuitive; instead of using a precise mathy scoring system, just make a guess. In my view, if their stated probability is 99.9% and your degree of belief is 90%, that merits an upvote: it's a pretty big difference of opinion. If they're at 99.9% and you're at 99.5%, it could go either way. If you're genuinely unsure whether or not you basically agree with them, you can pass on voting (but try not to). Vote up if you think they are either overconfident or underconfident in their belief: any disagreement is valid disagreement.
That's the spirit of the game, but some more qualifications and rules follow.
If the proposition in a comment isn't incredibly precise, use your best interpretation. If you really have to pick nits for whatever reason, say so in a comment reply.
The more upvotes you get, the more irrational Less Wrong perceives your belief to be. Which means that if you have a large amount of Less Wrong karma and can still get lots of upvotes on your crazy beliefs then you will get lots of smart people to take your weird ideas a little more seriously.
Some poor soul is going to come along and post "I believe in God". Don't pick nits and say "Well in a a Tegmark multiverse there is definitely a universe exactly like ours where some sort of god rules over us..." and downvote it. That's cheating. You better upvote the guy. For just this post, get over your desire to upvote rationality. For this game, we reward perceived irrationality.
Try to be precise in your propositions. Saying "I believe in God. 99% sure." isn't informative because we don't quite know which God you're talking about. A deist god? The Christian God? Jewish?
Y'all know this already, but just a reminder: preferences ain't beliefs. Downvote preferences disguised as beliefs. Beliefs that include the word "should" are are almost always imprecise: avoid them.
Additional rules: