144 Mr. TOZER, on THE FORCE OF TESTIMONY 



" Whenever the probability is of a definite and limited nature, (whether in the proportion of 

 one hundred to one, or of one thousand to one, or any other ratio, is immaterial), it cannot be 

 safely made the ground of conviction ; for to act U])on it in any case would be to decide, that 

 for the sake of convicting many criminals, the life of one innocent man might be sacrificed." 57-i- 



" The distinction between evidence of a conclusive tendency which is sufficient for the pur- 

 pose, and that which is inconclusive, appears to be this : the latter is limited and concluded by 

 some deo-ree or other of finite probability, beyond which it cannot go ; the former, though not 

 demonstrative, is attended with a degree of probability of an indefinite and unlimited nature" Ibid. 



Tlie above short passages are cited as containing a clear enunciation of the propositions dis- 

 sented from, and not as affording a complete exposition of the author's views, for which the 

 work itself is referred to. 



A passage from Lord Brougham's Natural Theology is also cited to by Mr. Wills, as includ- 

 ing the noble author among the advocates of the truth of the last of these propositions; it does 

 not however appear to do so. If the propositions are true, the conclusions here arrived at must 

 be erroneous. 



The expression of the value of a probability numerically is a necessary consequence of any 

 attempt to express that value accurately : if a certain event has been observed to accompany a 

 certain set of appearances more frequently than the appearances have been observed to occur without 

 the occurrence of the event, we may say that a repetition of the appearances creates a probability 

 of the repetition of the event — we may even say that that probability is great or small ; but if we 

 wish to say how great or how small, we are immediately forced on the enquiry, how many times 

 have the appearances to our knowledge occurred, and, out of these, how many times has the event 

 accompanied them. That the fraction which expresses the ratio of these numbers measures the pro- 

 bability of the occurrence of the event accompanying the appearances, is a consequence of the 

 definition of the term " probability ;" and if the term " moral probability" have any other definition, 

 that definition remains yet to be enunciated. 



If the appearances are of ordinary occurrence, or capable of being resolved into others which are 

 so, the fact that tlie particular combination may never before have been presented to the senses of 

 the person deciding, is not material ; the conceiving that if they were repeated a certain number of 

 times the event would accompany them a certain other number of times, is a process essential to the 

 conception of measuring the probability at all. If, again, the appearances afford some probability 

 of the event, but are so unusual that the judgment hesitates to assign the definite numbers it assigns 

 in the previous cases, the process is only varied to this extent : instead of assigning a numerical mea- 

 sure to the probability itself, we assign numerical values to the limits within which it lies. The 

 measure here then is indefinite, but it is so because, to the imperfect experience of the observer, the 

 probability is so; the indefiniteness has not been introduced in the process of measurement: the 

 least value also that the judgment assigns to the measure of the probability may be large enough 

 to measure a moral certainty, or the greatest so small that the probability must in ordinary occur- 

 rences be disregarded, without expanding or narrowing the limits through which indefiniteness may 

 range. If the probability be conclusive, its conclusiveness depends on the magnitude of the least 

 possible value of its measure; if it raise but a "light presumption," it would do so if the measure 

 of the highest limit were that of the probability itself. Suppose, for example, a medical witness to 

 assert, that certain appearances had led him to the conclusion that a person had died from taking 

 hydrocyanic acid. To determine then whether the allegation possesses the degree of probability 

 which would warrant our treating the fact alleged as true, we estimate the ability generally of the 

 witness to judge, his opportunities of judging in the particular case, and his sincerity. The phe- 

 nomenon then that we witness is that of a man possessing the ability and the inclination to speak 

 correctly, which the values we assign to these would confer on this particular witness making this 

 particular allegation; if then in our opinion this phenomenon would in 997 cases out of 1000 be 

 produced by the fact asserted, and in three cases out of 1000 by some other cause, and if we have 



