xlvi Appendix. 



On Prohahility. — (Part I.) By the Rev. R. Kidd, LL.D. 

 [Read before the Auckland Institute, Ist June, 1874.] 



1. There are two portions of the science of Probability which it is the aim 

 of the following observations in some degree to elucidate. Our present 

 inquiry will be as to the exact nature and relations of what we term Proba- 

 bility, a subject which is, I think, partially involved in confusion. On a 

 subsequent occasion we may consider a certain application of the calculus, 

 which appears to me to merit some development, and which has been hitherto 

 unnoticed in almost every treatise on Probability. 



2. (Popular signification of Prohahility.) — In common discourse we ascribe 

 probability to a proposition only when we regard it as not certainly true, but 

 more likely to be true than to be false. The term " probability," as thus used, 

 is equivalent to likelihood or verisimilitude. We find, accordingly, that this is 

 not the primary signification in that language, the Latin, from which the word 

 is derived ; and it will not be irrelevant to advert for a moment to its 

 earliest import. Indeed the primary meaning of the word will be found to 

 illustrate very appositely our determination of its present significance. The 

 root 2^foh denoted approhation ; to be probable, 2^^'ohahilis, was to be worthy of 

 being approved. In the classical Latin writers the word has both of these 

 significations, viz., app)rovahle and likely ; while the primary meaning alone 

 pertains to the cognate words prohus, prohitas, as to our English prohity^ 

 approhation. We may perceive how the secondary sense flowed from the 

 primary, when we consider that occasions of deliberation respecting the choice 

 of one or other course of action would be, in primitive states of society, almost 

 the only occasions of attempting to prove a proposition ; and that the most 

 approvahle course is that from which a good result is the most prohahle. 

 Demonstrations or proofs were not demanded, in primitive times, for history, 

 theology, jurisprudence, or any science ; but in all eras of human affairs the 

 meed of approbation is awarded to "sage counsel in cumber." 



3. ( Scientific Signification.) — In technical phraseology yet another appli- 

 cation of the term Probability has become established. In this wider 

 signification probability is recognized as pertaining to every proposition of 

 which wo do not know either the truth or the falsity. The grades of philo- 

 sophic probability include downwards all that we consider possihle ; and they 

 range up to all of which we do not consider the contrary to bo impossible. 

 And certainly it is fitting to have some designation which shall be thus widely 

 generic. Between the lowest possibility and the state of equipoise of evidence, 



