A Treatise of Human Nature · Chapter
Section XII: Of the Probability of Causes explained
Hume examines how we reason about causes when past experience shows contrary effects.
What happens
Hume examines how we reason about causes when past experience shows contrary effects. He argues that our inferences are not based on reason but on habit and custom, which produce a belief that the future will resemble the past. When past experiments are contrary, the mind's determination is broken into pieces, and the force of the impression is diffused over the various images, leading to a weaker belief proportional to the number of contrary instances. He also discusses the role of analogy and general rules in probabilistic reasoning, noting that even minute differences in probability influence our judgment through custom rather than through direct perception.
Themes in this chapter
Custom and General Rules
Hume emphasizes that our belief in the future resembling the past is derived entirely from habit, and that general rules, not direct perception, guide our judgments in cases of minute differences in probability.
Skepticism About the External World
Hume argues that there is nothing in any object, considered in itself, that can afford a reason for drawing a conclusion beyond it, and that even after observing constant conjunction, we have no reason to infer anything beyond our experience.
Association of Ideas
The chapter discusses how the mind associates ideas through resemblance and constant conjunction, and how the force of these associations is weakened when the conjunction is not constant or the resemblance is imperfect.
Characters to notice
- David Hume
Author and narrator, presenting his philosophical analysis of probability and causation.
Key passages
“But however philosophers and the vulgar may differ in their explication of the contrariety of events, their inferences from it are always of the same kind, and founded on the same principles.”
Whether philosophers or ordinary people explain the uncertainty of events differently, they all draw the same kind of conclusions from it, based on the same underlying principles.
Hume highlights the universal nature of probabilistic reasoning despite differing explanations.
“When we follow only the habitual determination of the mind, we make the transition without any reflection, and interpose not a moment’s delay betwixt the view of one object and the belief of that, which is often found to attend it.”
When we rely solely on habit, we move from seeing one thing to believing in its usual effect without any conscious thought or delay.
This illustrates the immediate operation of custom in our reasoning.
“Let men be once fully persuaded of these two principles, That there is nothing in any object, considered in itself, which can afford us a reason for drawing a conclusion beyond it; and, that even after the observation of the frequent or constant conjunction of objects, we have no reason to draw any inference concerning any object beyond those of which we have had experience.”
If people fully accept that no object by itself gives us a reason to infer something beyond it, and that even repeated observations of constant conjunction don't justify inferences about unobserved cases, they will be open to any extraordinary philosophical system.
Hume's core skeptical principles about causation and induction.
“The difference, therefore, of our conduct in preferring the greater number depends not upon our passions, but upon custom, and general rules.”
Our tendency to prefer a larger number over a slightly smaller one is not due to our passions, but rather to custom and general rules that we apply from past experience.
Hume explains how general rules influence our judgments even when we cannot directly perceive the difference.