An argument can be "decent" without being right. If you want an example, and can follow it Kurt Godel's ontological argument looks pretty decent. Consider that:
A) It is a logically valid argument
B) The premises sound fairly plausible (we can on the face of it imagine some sense of a "positive property" which would satisfy the premises)
C) It is not immediately obvious what is wrong with the premises
The wrongness can eventually be seen by carefully inspecting the premises, and checking which would go wrong in a null world (a possible world with no entities at all). Axiom 1 implies that if an impossible property is positive, then so is its negation (since an impossible property logically entails its negation). Axiom 2 says that can't be true - a property and its negation can't both be positive. So together these are a coded way of saying that all positive properties are possible properties. And then Axiom 5 (Neccessary existence is a positive property) goes wrong, because necessary existence is not a possible property in the null world. So it is not a positive property. Axiom 5 is inconsistent with Axioms 1 and 2.
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* Normal_Anomaly
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A note for theists: you will find the Less Wrong community to be predominantly atheist, though not completely so, and most of us are genuinely respectful of religious people who keep the usual community norms. It's worth saying that we might think religion is off-topic in some places where you think it's on-topic, so be thoughtful about where and how you start explicitly talking about it; some of us are happy to talk about religion, some of us aren't interested. Bear in mind that many of us really, truly have given full consideration to theistic claims and found them to be false, so starting with the most common arguments is pretty likely just to annoy people. Anyhow, it's absolutely OK to mention that you're religious in your welcome post and to invite a discussion there.
A list of some posts that are pretty awesome
I recommend the major sequences to everybody, but I realize how daunting they look at first. So for purposes of immediate gratification, the following posts are particularly interesting/illuminating/provocative and don't require any previous reading:
More suggestions are welcome! Or just check out the top-rated posts from the history of Less Wrong. Most posts at +50 or more are well worth your time.
Welcome to Less Wrong, and we look forward to hearing from you throughout the site!
Note from orthonormal: MBlume and other contributors wrote the original version of this welcome post, and I've edited it a fair bit. If there's anything I should add or update on this post (especially broken links), please send me a private message—I may not notice a comment on the post. Finally, once this gets past 500 comments, anyone is welcome to copy and edit this intro to start the next welcome thread.