Natural philosophy. An essay on probabilities and their application to life contingencies and insurance offers by Augustus De Morgan.

  • De Morgan, Augustus, 1806-1871.
Date:
1841
Catalogue details

Licence: Public Domain Mark

Credit: Natural philosophy. An essay on probabilities and their application to life contingencies and insurance offers by Augustus De Morgan. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    their being false. However improbable it may be, for in- stance, that the barbarians did not overturn the Roman empire, we do not recognise the same sort of sensible cer- tainty in our moral certainty of the fact which we have in our knowledge that fire burns, or that two straight lines do not enclose space. And we perceive a difference in the quality of our knowledge, when any alteration takes place in our circumstances with respect to exterior objects. That fire does burn is more certain than the account of the fall of Rome: that fire yet to be lighted will burn may or may not be more certain than the historical fact, according to the temperament and knowledge of the in- dividual. And thus we begin to recognise differences even between our (so called) certainties; and the com- parative phrases of more and less certain are admissible and intelligible. It is usual to begin the subject by saying that our certainties are only very high degrees of probability. This is not practically true at the outset; yet so far as deductions can be made numerically, with respect to our impressions of assent or dissent, it will be shown to be correct so to consider the subject. We have a process to go through before we can arrive at such a conclusion, as follows : —When a child is born, there is a certain degree of force which we allow to the assertion that he will die aged 50. To it we answer that it may be, but that that particular age is unlikely compared with all the rest, though, at first sight, as likely as any other. If the assertion be made of two children, that one or other will die aged 50, we readily admit that our “it may be, but it is not likely,” is no longer the same assertion as it was before, it is of the same sort, but not of the same strength : the assertion is more probable, and wherever we have the notion of more and less, we feel the possibility of an answer to the question, “ how much more or less ? ” and which we should produce if we knew how. First impressions would induce us to suppose it twice as probable that the assertion may be made of one or other of two children, as of one alone; and so on. Let this false measure (for b 2