Dr. Ari Santas Notes on

Hume, Section IX: Of the Reason of Animals


A.     Analogy and Custom

We have already seen that custom, for Hume, is the foundation of all causal reasoning

But we must recognize that a condition for forming this mental habit is being able to see different events as similar

For this reason, Hume acknowledges that all our reasonings concerning matters of fact depend on a species of analogy

Given this, we can evaluate the legitimacy of any given causal inference on these criteria:

1)      Custom: how strong is the habit (how constant is the conjunction)?

2)      Analogy: how similar is the present event to those events in your past experience (to which you are accustomed)








Relations of Ideas Fields of Inquiry Matters of Fact



Pure Reason Type of Reasoning Experimental Reason



Principle of Guiding Principles Analogy and Custom




Logical Nature of Evidence Complete/Incomplete



Demonstration Proof or Probability

(a priori) (a posteriori)