Personal criticisms and logical fallacies

[Steven Howe]

Really, is this a relevant topic on a program mail list? You guys need 
to get a room and start discussing angel counts on pinheads under the 
blankets.

sph

On 02/09/2010 10:51 PM, D'Arcy J.M. Cain wrote:
> On Wed, 10 Feb 2010 01:38:50 +0100
> "Alf P. Steinbach"<alfps at start.no>  wrote:
>    
>> However, although in this particular case the Ad Hominems constituted logical
>> fallacies, not all Ad Hominems are logical fallacies.
>>      
> Yes they are.  Using the reputation of someone to prove or disprove
> their claims is a logical fallacy.
>
>    
>> For example, if a person is a chronic liar, has a known history of lying, then
>> that can have a strong bearing on whether the person's claims  --  technical or
>> about other persons  --  should be seriously considered[1].
>>      
> Yes but it's still a fallacy.  Taking the author's history into account
> may be valid for deciding that further investigation is warranted but by
> itself it does not prove anything about the claims.  Suggesting that it
> does is fallacious.
>
> "Bill is a liar therefore his statement is false" is a fallacy.  "Bill
> is a liar so take his claims with a grain of salt" is not.
>
> There is another case.  "Bill never tells the truth therefore his
> claim is wrong" is not an ad hominem fallacy.  It's a sylogism.  It may
> or may not be correct but if the first statement is true (Bill always
> lies) then the the conclusion is true.
>
>