DEGKEES OF PKOBABILITY IN SCIENCE. 151 



in nature are results of unerring laws, probability, uncer- 

 tainty, or chance has no existence in them ; and if all our 

 capacities for perceiving and understanding nature were 

 coextensive with nature itself, all our scientific beliefs 

 would be certain, and we should not require to express 

 any natural event in terms of proportionate truth. 



The degree of probability with which we regard an 

 event depends largely upon our knowledge and experience ; 

 we are apt to miscalculate the true degree of probability 

 of that of which we have no experience or knowledge. 

 Our estimate of probability, like that of accuracy, is 

 therefore a thing of degree, and depends upon the suffi- 

 ciency of the evidence, and our capacity for receiving and 

 understanding it. 



Probability is a very important and extensive subject 

 in science ; and, according to Butler, it 4 is the very guide 

 of life.' As our knowledge of nature is extremely imper- 

 fect, the element of probability enters into nearly all our 

 thoughts and acts : and as the data from which we reason 

 are very rarely certain, our inferences are often only pro- 

 bable, and we require to know the degree of probability of 

 statements before we reason upon them. In this way a 

 knowledge of probability is a necessary basis of inference 

 and a guide of conduct. 



Our inferences of future events are all of them pro- 

 bable only, because of our finite experience and know- 

 ledge ; but the degree of probability of an event is often 

 sufficient to remove all serious degree of doubt. That 

 which is very nearly certain, we accept as certain, in order 

 to save us further labour ; and as it is sufficiently certain 

 for nearly all practical purposes, we usually act upon it 

 and incur the risk. 



Scientific hypotheses are often only probably true, and 

 that in a small degree ; but we must not reject or even 



