1. David Hume’s Skepticism The nature of ideas and reasoning concerning ‘matters of fact’

2. David Hume 1711-1776  Prolific and successful writer on philosophy, history and economics; published his Treatise at the age of 26.  Never held a university position (he was suspected of atheism).  The French called him ‘le bon David’.

3. Empiricism  Hume is called an empiricist, because of the emphasis he and his fellow empiricists placed on the contribution of experience to our knowledge.  Descartes is called a rationalist: he and his fellow rationalists emphasized the importance of fundamental principles of thought that he regards as a priori, that is, as knowable independent of experience.

4. The source of ideas  For Hume ideas are merely faint images or copies of much more vivid experiences – perceptions of the senses and emotional states.  This difference in ‘liveliness’ (force or vivacity) is the real difference between the weaker states of mind we call ‘ideas’ and other ‘perceptions of the mind’, which Hume proposes to call ‘impressions’.

5. The imagination  According to Hume we can freely combine our ideas in almost unlimited ways.  But the basic materials that we combine and rearrange so freely depend strictly on experience, i.e. on having previously had an impression, of which our idea is a kind of pale, weak copy.  Consider the contrast between Hume’s account of the idea of God and Descartes’.

6. Arguing for the view  If you disagree, says Hume, give me an example of an idea that doesn’t depend on experience in this way!  We find, whenever someone lacks a sense (sight, e.g.) or the opportunity to experience something (the dry Laplander, the mild mannered man), they also lack the corresponding ideas.

7. One contrary case  The missing colour: Given a complete sequence of shades with one gap where a shade is omitted, we seem able to imagine what that shade is like, i.e. to form the idea of that shade. Hume thinks this exception is so ‘singular’ that the general principle should be retained.  What allows this to happen? Can we think of any other such cases?

8. A method for inquiry  Since impressions are always more lively and clear, when we try to think about any idea (or the meaning of any philosophical term), we should always try to trace it back to the ‘impression from which it is derived’.  If we can’t do this, we are justified in suspecting that the term ‘is employed without any meaning or idea’.

9. Operations of the Understanding  Relations of ideas: Geometry, Algebra, Arithmetic… Affirmations that are ‘intuitively or demonstratively certain’.  Matters of Fact: The contrary of these is possible. Can’t demonstrate such facts (otherwise their contraries would be contradictions and ‘could never be distinctly conceived by the mind’).

10. The Sun  The Sun will not rise tomorrow.  Though we’re sure this is false, we can’t demonstrate that it is (to do so requires showing that it’s somehow contradictory, but it isn’t: we can distinctly conceive this happening).  So we have a puzzle: “(W)hat is the nature of that evidence which assures us of any real existence and matter of fact beyond the present testimony of our senses or the records of our memory?”

11. Cause and Effect  The basis of all reasoning concerning matters of fact.  This is the link that connects any present or remembered facts to other facts that we infer from them.  (It also links our memories to the facts they are memories of.)  So how do we come by our knowledge of cause and effect?  Hume says we have no a priori grounds for this– only experience can do the job.

12. An argument  No one can tell what the effects (or causes) of an entirely new and unfamiliar sort of thing will be.  Adam could not have known, simply from looking at it or feeling it, that water would suffocate him or fire burn him.  Familiar causes and effects may seem, to us, to be obvious– but only experience makes them so (the billiard table).  How could the mind supply us with such information on its own? There are no necessary relations between (separate) facts!

13. Trouble  Now, how do we reason from experience to our conclusions about cause and effect?  Is this reasoning any good?  Hume is worried!  He says, ‘even after we have experience of the operation of cause and effect, our conclusions from that experience are not founded on reasoning or any process of the understanding’. (225)

14. Like causes, like effects?  “We always presume when we see like sensible qualities that they have like secret powers.”  Past experience applies only to those particular objects and situations.  It just doesn’t follow that similar objects and situations will produce similar results. No reasoning justifies this expectation.

15. Experience and reason don’t do it.  If something about a pattern of events shows that the pattern was necessary, we should see it (and be able to reason it out) the first time we experience the pattern.  Yet we don’t reach the conclusion that the pattern must be followed in every instance when we first see it. We need repeated experience to reach this conclusion.

16. What does needing repetition show?  If some kind of argument links cause to effect, then we should be able, once we’ve clearly grasped the cause, to infer that the effect must follow.  If the argument infers a ‘necessary connection’ from the experience of a repeated pattern, Hume asks what this ‘medium’ joining cause and effect is supposed to be, and how repetition leads us to detect it?

17. Furthermore, it should be obvious  Animals and babies clearly reach these kinds of conclusions too.  So any reasoning (or experience) that tells us a pattern will continue should be obvious when we think about it.  “… if I be wrong (i.e.there is an argument linking cause to effect)…I cannot now discover an argument which…was perfectly familiar to me …before I was out of my cradle.”

18. What could repetition add?  Hume’s view is that the only thing repetition of the pattern could do for us is to build a pattern in us, a habit of regularly expecting the effect whenever we witness the cause.  Hume concludes that the experience of persistent, regular patterns leads us to form this kind of habitual expectation.  But there’s no justification we can give for this expectation; it really is just a habit.

19. The regress.  Hume asks what sort of justification we could give, of basing our expectations about the future on the experience of regular patterns in the past.  The only justification available seems to be that we’ve been successful, in the past, when we do this, i.e. these expectations have proven right.  But that’s just another past pattern, and the question here is what reason we have to think that past regular patterns will continue into the future!

20. Skeptical Modesty  Hume defends a skeptical response to this puzzle.  Even though there is no reason to expect the future to resemble the past, nature leads us to this expectation.  A calm, skeptical attitude fits perfectly here: we accept that we have no good reason for this expectation, but we have the expectation anyway.