Dr. Ari Santas’ Notes on

Hume’s Enquiry VI: Of Probability


A.     Three Kinds of Certainty

·  Up to the time of Hume, most philosophers had distinguished between two forms of certainty


the                    Demonstration                                      Probability                    the

objects                                                                                                             objects

of                     Absolute Certainty                                Uncertain                      of        

knowledge                                                                                                        belief

                  Necessary                                            Contingent


                  Reason                                                 Experience


·  Hume says this is a false dichotomy and adds a third candidate


Demonstration                          Proof                            Probability


logically                                    empirically                    contingent

necessary                                 necessary


cannot be                                 uncontradicted chance

otherwise                                  by experience               (not entirely

                                                (entirely uniform)             uniform)




                                                                degrees of legitimacy


B.     Proof and Probability

·  Leaving knowledge to the rationalists, Hume focuses on belief and considers how we arrive at it

      ·  It is based on experience, in particular, past experience

      ·  Repetition in experience creates habit

      ·  Experienced patterns fashion belief

·  When these patterns are entirely uniform we say that the belief has proof behind it

      ·  It has always happened that way, so I believe it

·  When these patterns are less than completely uniform, we say there is a probability

      ·  It sometimes happens that way

·  Neither carries apodictic certainty, but we say some beliefs are better than others


C.     A Normative Model of Belief

      ·  A wise man, then, proportions his belief to evidence

      ·  When the pattern is complete, we must infer that the same will occur in the future

            ·  The Laws of Nature

·  When the pattern is incomplete, we must suspend belief, how much depending on how complete or incomplete the pattern

      ·  Degrees of uniformity    >    Degrees of Certainty

·  To believe well, then, we need to observe carefully, look for patterns, and infer accordingly



Overview of Sections I-VI


Let us introspect on Consciousness (I)



Ideas come from Impressions (II)



By Memory                  And the Imagination

(II)                                                                              (II)



By Combining and Dividing                               By Association  (III)




                                                Resemblance                Contiguity                     Causation



                                                             Made Possible by Custom, not Reason                       

                                                                                    (IV, V)



                                                     Resulting belief is (and should be) proportionate

                                                            to the uniformity of experience (VI)


D.     Reconstructing the Guiding Principles

·  All knowledge of the world ultimately boils down to impressions, our ability to associate ideas from habit

·  In that sense, the ultimate principle of reasoning about the world is not rational - it is a feeling that accompanies a habit

·  The traditional Principles of Rationality have been modified or curtailed

·  Principles of Contradiction cannot discover things about the world - only deduce things given relations supplied by experience

            ·  Principle of Sufficient Reason is limited to what we have experienced

·  PSR revision: everything in experience has a cause, where cause means an associated idea and not a reason as in ultimate explanation