An argument is valid when it contains no logical fallacies. Such arguments are not necessarily sound, because the premises may be false. For instance, the following syllogism is valid but has a false conclusion:
All animals are dogs. (False premise/All A are B.)
All dogs are terriers. (False premise/All B are C.)
Thereforse, all animals are terriers. (False conclusion: not all animals are terriers. Valid logic: If all A are B, and all B are C, then all A are C.)
Blog posts
The Parable of Hemlock (tangentially related)
From the old discussion page:
Talk:Valid argument
Citation needed (for it being a settled usage and not just terminology made up on the spot). Again, I don’t see enough notability to keep this article (the same goes for Sound logic). Unless you convince me, I’m going to remove it (in a few days). Please don’t create articles of little use, this only increases bit rot. As it is, the wiki needs more quality and detail for the existing articles, not more raw material (see my user page). --Vladimir Nesov 16:31, 22 January 2011 (UTC)
Citation? This is an age-old distinction in logic, distinguishing between a valid and a sound proof. Introductory philosophy courses often cover as do introductory logic textbooks. Wikipedia even covers it: http://en.wikipedia.org/wiki/Validity#Validity_and_soundness—Gwern 17:24, 22 January 2011 (UTC)
Yes, somehow I forgot this usage, as applied to arguments, and assumed I wouldn’t if it was standard (the usage of “sound logic” as opposed to “sound argument” was another factor, renamed), so the problem of the terms being non-standard is no more. I still think the concepts are not particularly relevant to LW, since they rarely come up in discussion and there are hardly any posts starring them, but won’t remove them since they are standard and articles are now in an OK form. Also, I don’t see how to link to them from other pages, which is another piece of evidence for them not being LW relevant. --Vladimir Nesov 20:16, 22 January 2011 (UTC)