Hume

David Hume
From Introspection to Skepticism 

  • Philosopher, economist, historian, and essayist
  • Led the Scottish Enlightenment with his friend Adam Smith
  • Tried to develop a scientific theory of human nature, which paradoxically led to skepticism.
  • Philosophic Works
    • Treatise of Human Nature 1739
    • Enquiry Concerning Human Understanding 1748, 1758
    • Enquiry Concerning Principles of Morals 1751
    • Dialogues Concerning Natural Religion 1779
  • Themes
    • Relations of Ideas and Matters of Fact
    • Two Kinds of Reasoning
    • Skepticism
    • Causation

Themes
  • Relations of Ideas and Matters of Fact
    • No matter of fact can be known a priori. Hence, Rationalism is false.
  • Two Kinds of Reasoning
    • Demonstrative
    • Probable
  • Skepticism
    • External World
      • There’s no rational basis for believing that sense-perceptions are caused by material objects resembling them.
    • Problem of Induction
      • There’s no rational basis for believing that what’s true of observed cases is true of unobserved cases.
    • Miracles
      • Testimony is not a rational basis for believing a miracle has occurred
  • Causation
    • A cause doesn’t “necessitate” its effect or “make” it happen.
    • Analysis of Causation
Relations of Ideas and Matters of Fact
  • Leibniz had introduced the distinction between truths of reason and truths of fact. Hume drew the same distinction, using the terms relations of ideas and matters of fact.  But Hume went further, using the distinction to argue that Rationalism is false. 
  • Relations of Ideas
    • Relations of ideas are propositions that are “either intuitively or demonstratively certain. That the square of the hypotenuse is equal to the square of the two sides, is a proposition which expresses a relation between these figures. That three times five is equal to the half of thirty, expresses a relation between these numbers. Propositions of this kind are discoverable by the mere operation of thought, without dependence on what is anywhere existent in the universe. Though there never were a circle or triangle in nature, the truths demonstrated by Euclid would for ever retain their certainty and evidence. “ (EHU 20)
  • Matters of Fact
    • “Matters of fact …are not ascertained in the same manner [as relations of ideas]; nor is our evidence of their truth, however great, of a like nature with the foregoing. The contrary of every matter of fact is still possible; because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if ever so conformable to reality. That the sun will not rise tomorrow is no less intelligible a proposition, and implies no more contradiction than the affirmation, that it will rise. We should in vain, therefore, attempt to demonstrate its falsehood. Were it demonstratively false, it would imply a contradiction, and could never be distinctly conceived by the mind.”  (EHU 21)
  • Relations of ideas are knowable a priori
    • Relations of ideas “include every affirmation which is either intuitively or demonstratively certain.” (EHU 20)
    • “Propositions of this kind are discoverable by the mere operation of thought, without dependence on what is anywhere existent in the universe” (EHU 20)
  • Matters of fact are not knowable a priori
    • A proposition can be known a priori only if its negation implies a contradiction.
    • The negation of a matter of fact does not imply a contradiction.
    • Therefore, a matter of fact cannot be known a priori.
  • Corollaries
    • Rationalism is false.
    • Matters of fact can only be known a posteriori, through experience.
Two Kinds of Reasoning
  • “All reasonings may be divided into two kinds, namely, demonstrative reasoning, or that concerning relations of ideas, and moral [i.e. probable] reasoning, or that concerning matter of fact and existence.”
    • Hume (E. 4.2.18)
  • Demonstrative Reasoning
    • Demonstrative reasoning is reasoning concerning relations of ideas.
    • For example, mathematical proofs.
  • Probable Reasoning
    • Probable reasoning is reasoning concerning matters of fact.
    • It is “founded on the relation of cause and effect”
Skepticism
External World
  • Hume’s Argument from EHU 119, Paraphrased
    • It is a question of fact whether sense perceptions are produced by external objects resembling them, as opposed to by
      • the energy of the mind itself
      • some invisible and unknown spirit
      • [a computer with electrodes attached to your brain]
    • Questions of fact are determined by experience.
    • But the mind cannot have an experience of a connection between sense perceptions and external objects because the mind experiences only perceptions. 
    • Therefore, the mind can’t determine whether sense perceptions are caused by physical objects.
    • Therefore there’s no rational foundation for believing sense perceptions are produced by external objects resembling them.
Inductive Inference
  • Hume’s argument that there’s no rational basis for believing any “matter of fact beyond the present testimony of our senses, or the records of our memory.” from EHU Section IV, Part II, Paraphrased
    • Reasoning concerning matters of fact is founded on the relation of cause and effect
    • Reasoning concerning cause and effect is founded on experience.
    • Reasoning concerning experience presupposes that it is rational to believe the future will resemble the past.
    • To be rational to believe, the presupposition must be founded on either demonstrative reasoning concerning relations of ideas or probable reasoning concerning matters of fact.
    • It is not founded on demonstrative reasoning because there is “no contradiction that the course of nature may change, and that an object, seemingly like those which we have experienced, may be attended with different or contrary effects.”
    • The presupposition must therefore be founded on probable reasoning concerning matters of fact.
    • “To endeavor, therefore, the proof of this last supposition by probable arguments, or arguments regarding existence, must be evidently going in a circle, and taking that for granted, which is the very point in question.” (Hume)
    • That is:
      • To prove the presupposition, that the future will resemble the past, the presupposition must be founded on probable reasoning concerning matters of fact, which is founded on the relation of cause and effect, which is founded on experience, which presupposes that it is rational to believe the future will resemble the past.
      • Thus, to prove that the future will resemble the past it must be rational to believe the future will resemble the past.
  • Example:
    • Suppose you infer that black swans exist from the Britannica’s article on swans.
    • Your inference is:
      • The Britannica is a reliable source of information.
      • The Britannica says there are black swans.
      • Therefore it’s reasonable to believe there are black swans.
    • The foundation for believing that the Britannica is a reliable source of information is that:
      • The Britannica is rarely wrong
      • The reasons for its reliability are understood, e.g. how its editing process minimizes the risk of misinformation
    • The foundation for believing the Britannica is rarely wrong is that it has been rarely wrong in the past.
    • The foundation for believing that the reasons for its reliability are understood is that the reasons for its past reliability are understood.
    • Thus the foundation of your inference that black swans exist is ultimately that
      • The Britannica has been rarely wrong in the past
      • The reasons for its past reliability are understood.
    • But the foundation of your inference also includes the presupposition that the Britannica’s past reliability extends to your inference, that is, that the present resembles the past.
    • But there’s no rational foundation for the presupposition.
Miracles
Philosophic and Practical Skepticism
Causation
  • A cause doesn’t “necessitate” its effect or “make” it happen.
    • Hume’s argument uses his Copy Principle, that every (simple) idea is a copy of an impression
      • Impressions include “outer sense-perceptions” and “inner perceptions” such as kinesthetic sensations, feelings, urges, hunger pangs, emotions.
      • Examples of the Copy Principle:
        • The idea of red is a copy of your sensations of red.
        • The idea of anger is a copy of your feelings of anger.
    • Hume’s argument:
      • Every idea is a copy of an impression (Copy Principle)
      • There are no impressions of making-happen or necessitation
        • When you see the cue ball hit the eight ball, you have sense-impressions of the cue ball moving, the cue ball hitting the eight ball, and the eight ball moving.  But you have no sense-impression of the cue ball making or necessitating the eight ball move.
      • Thus, there is no idea of making-happen or necessitation.
      • A word is meaningless if it doesn’t express an idea.
      • Hence, the words “making happen” and “necessitate” are meaningless
      • A cause therefore doesn’t “necessitate” its effect or “make” it happen.
  • Analysis of Causation
    • If a cause doesn’t make its effect happen, what is causation?
    • Hume’s answer:
      • “We may define a cause to be an object, followed by another, and where all the objects similar to the first are followed by objects similar to the second”
    • For Hume, the cue ball hitting the eight (on a particular occasion) causes the eight ball to move means
      • the cue ball hitting the eight (on this occasion) is followed by the eight ball moving, and
      • in general, a billiard ball hitting a second billiard ball is followed by the second billiard ball moving.
In Sum
  • Hume is ranked among the greatest philosophers, for good reason. His arguments are clear, cogent, and insightful. His writings memorable:
  • From Of Miracles:
    • “In our reasonings concerning matter of fact, there are all imaginable degrees of assurance, from the highest certainty to the lowest species of moral evidence. A wise man, therefore, proportions his belief to the evidence.”
  • The final paragraph of An Enquiry Concerning Human Understanding:
    • “When we run over libraries, persuaded of these principles, what havoc must we make? If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: For it can contain nothing but sophistry and illusion.”