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For the fame reafon, the probability of its failing will be equal 

 to the number of chances for its failing, divided by the fum of 

 the number of chances of happening and failing together. 



The probability therefore either of the happening or failing of 

 an event is always expreffed by a proper fradion. 



If the number of chances of happening be = o, that is, if the 

 event be impoffible, the numerator, and therefore the fradion 

 will be = o J o therefore denotes impoflibility.^ 



If the number of chances of failing be = o, that is, if the event 

 be certain, the numerator will be equal to the denominator, and 

 the fradion = i ; unity therefore expreffes certainty. 



Probability therefore extends, as Mr. Locke obferves, from 

 certainty to impoffibility. 



When the chances for the happening of an event are equal to 

 the chances of its failing, the fradion, exprefling the probability, is 

 = ^, which is the mean between impoifibility and certainty. 



One event therefore is faid to be more probable than another 

 when its probability is expreffed by a greater fradion ; though, in 

 the common acceptation of the word, that only is faid to be pro- 

 bable, whofe probability exceeds half certainty ; for if the proba- 



L % bility 



