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bability, the probability of the conclusion is the product of the pro- 

 babilities of the premises, in those cases only where the presence of 

 the middle term is necessary for the connexion of the major and 

 minor terms. When this is not so, then the probability of the con- 

 clusion is the product of the probabilities of the premises, plus the 

 sum of the probabilities arising from the other conceivable causes of 

 connexion. 



2. In a sorites of probable premises, any premise with a proba- 

 bility of ^ brings the force of the argument up to that premise in- 

 clusive to a probability of ^. 



3. When various arguments of different validities have been ad- 

 vanced for a proposition, or when evidence has been brought in sup- 

 port of argument, or argument of evidence, the resulting probability 

 is not the sum, but the average of the several pi'obabilities ; so that 

 a weaker argument following upon a stronger, w^eakens it, or rather 

 weakens the probability produced by it. 



