SECT. 3.] Testimony. 395 



2. It will be remembered that in the course of the 

 chapter on Induction we entered into a detailed investiga 

 tion of the process demanded of us when, instead of the 

 appropriate propositions from which the inference was to be 

 made being set before us, the individual presented himself, 

 and the task was imposed upon us of selecting the requisite 

 groups or series to which to refer him. In other words, in 

 stead of calculating the chance of an event from determinate 

 conditions of frequency of its occurrence (these being either 

 obtained by direct experience, or deductively inferred) we 

 have to select the conditions of frequency out of a plurality 

 of more or less suitable ones. When the problem is pre 

 sented to us at such a stage as this, we may of course assume 

 that the preliminary process of obtaining the statistics 

 which are extended into the proportional propositions has 

 been already performed ; we may suppose therefore that \ve 

 are already in possession of a quantity of such propositions, 

 our principal remaining doubt being as to which of them 

 we should then employ. This selection was shown to be 

 to a certain extent arbitrary ; for, owing to the fact of the 

 individual possessing a large number of different properties, 

 he became in consequence a member of different series or 

 groups, which might present different averages. We must 

 now examine, somewhat more fully than we did before, 

 the practical conditions under which any difficulty arising 

 from this source ceases to be of importance. 



3. One condition of this kind is very simple and ob 

 vious. It is that the different statistics with which we are 

 presented should not in reality offer materially different 

 results. If, for instance, we were enquiring into the pro 

 bability of a man aged forty dying within the year, we might 

 if we pleased take into account the fact of his having red 

 hair, or his having been born in a certain county or town. 



