<div><span class="gmail_quote">On 1/5/08, <b class="gmail_sendername">Harvey Newstrom</b> <<a href="mailto:mail@harveynewstrom.com">mail@harveynewstrom.com</a>> wrote:</span></div>
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<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">No, the purpose of deductive argumentation is to deduce further facts from<br>existing known facts. The major premise must be true for the argument to be
<br>true. If the major premise is assumed, it is called "begging the question"<br>or "circular logic" where the assumption is made first, and then the<br>argument is derived from the assumption.</blockquote>
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<div>He's trying to say the argument is meant hypothetically, as testing out the consequences from the premises. It actually does make sense, if you suspect a given conclusion to be true, to find a deductive argument for it to see if the necessary premises for it can be substantiated, and which premises are needed. Logic only cares about *logical* priority, it really doesn't care if you come across the conclusion or the premises first; and it certainly doesn't demand that premises can't be tested or tried out until you somehow have absolutely certainty that they are true.
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<div>And I think it's time to distinguish between soundness and validity. There's no logical meaning that I know of for an argument being "true". Validity just ensures that *if* the premises are true, then the conclusion is necessarily true. Soundness is when the argument is valid, the premises are all true, and the conclusion is therefore true. While it is great when an argument is sound, as that is usually the ultimate aim of the argument, it is really only the arguments in mathematics where we can have confidence in the soundness of arguments. Everywhere else, there's usually some measure of doubt.
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<div>Kevin</div></div>