The conclusion which denies its premises is one of the ‘oh-dear-l-forgot-what-l-started-to-say’ fallacies. It starts by maintaining that certain things must be true, and ends up with a conclusion which flatly contradicts them. If the conclusion is not consistent with the arguments used to reach it, then somewhere there is a hole in the reasoning through which the logic has slipped silently away.
‘Son, because nothing is certain in this world we have to hold on to what experience tells us.’
‘Are you sure, Dad?’
‘Yes, son. I’m certain.’
The fallacy is identified by the inconsistency. If the conclusion contradicts the premises, at least one of them must be wrong. This means that our conclusion is either false itself, or derived from false information.
The conclusion which denies its premises constantly slips uninvited into religious arguments. People are so used to thinking of divine beings as exceptions to every rule that they tend to use the word ‘everything’ when they mean ‘everything except God.’
Everything must have a cause. That, in turn, must result from a previous cause. Since it cannot go back forever, we know that there must be an uncaused causer to start the process.
(But if everything must have a cause, how can there be such a thing as an uncaused causer?)
The fallacy has a most distinguished history, being used (although not identified as such) by Aristotle and Thomas Aquinas among many others. It has many faces. The ‘uncaused causer’ can be a ‘first cause,’ or even a ‘first mover’. It can be reworded in many ways, but never without fallacy.
Attempts to make a divine being the allowable exception to the original claim usually beg the question or subvert the argument, ‘Everything in the universe must have a cause outside of itself ..The intention is clearly to establish a cause which is outside of the universe and therefore needs no cause to account for it. Unfortunately, the rewording admits several faults.
1. The new version is more complex and is not obviously true.
2. The universe is not in the universe, it is the universe.
3. ‘Everything in the universe’ is the universe.
This allows us to translate the opening line as: ‘The universe must have a cause outside of itself.’ Given such an assumption, it is hardly surprising that we go on to prove it.
There are many simpler versions in popular currency, none of them free from the basic inconsistency of allowing the preferred answer to be the one permitted exception.
No matter how many stages you take it back, everything must have had a beginning somewhere. Cod started it all.
(He, presumably, did not have a beginning somewhere.)
Nothing can go on forever. There must have been a god to start it.
(One who goes on forever, of course.)
When using the conclusion which denies premises, you should bear in mind three things. First, the more distance there is between your opening line and your conclusion, the less likely are your audience to spot the contradiction. Second, they will often allow a speaker to make statements about ‘everyone’ without applying them to the speaker himself. Third, if your conclusion is about things which are usually admitted to have exceptional properties, your fallacy has a better chance of escaping detection.
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The above article is from the book How To Win Every Argument by Madsen Pirie. The article is only for educational and informative purposes to explain and understand formal logic and logical fallacies. It is a great book, definitely worth a read!