David Hume on How Thoughts are Made and Mixed

David Hume thought a lot about how thoughts are made and mixed. His thoughts concerning such inquiries was summed up in the 1748 classic “An Enquiry Concerning Human Understanding.”

As far as titles go (refer to the title), it’s entitled to a bit of praise for it so accurately describes what follows. The “what” that follows is the subject of Human Understanding.

What is “understanding”? How do humans understand?


David Hume (1711 – 1776 for those who love births and deaths) was born in Edinburg and, 65 years later, dead in Edinburg. In the years between he wrote books on philosophy, history and economics (he was a friend of Adam Smith) and spent a lot of time in Parisian salons talking, dining, and drinking with other intellectuals.

Hume’s literary fame came through his multi-volume The History of England, a work that everyone read in his day yet no one does today. His posthumous fame came through his Treatisie and Enquiry, works that no one read in his day yet everyone does today.

His notorious reputation as an atheist and skeptic made it difficult to secure an academic position, so he chose the life of a public intellectual. Hume was articulate, opinionated, caring, witty, and great fun to be around.

He was concise too, considering he summed up his life in an autobiography of “fewer than 5 pages.”


  1. Our 5 senses create Impressions that give us knowledge of the world
  2. These impressions become thoughts through 4 operations: compounding, transposing, enlarging, and diminishing
  3. These thoughts relate with other thoughts through 3 associations: resemblance, contiguity, cause-and-effect
  4. These thoughts are either based on Matters-of-Fact and depend on what exists or Relations of Ideas and are independent of what exists.

Sense Perceptions

David Hume Impressions vs. Thoughts
David Hume distinguishes between Impressions and Thoughts

The Impressions that Hume wrote about are “all our more lively perceptions when we hear or see or feel or love or hate or desire or will.” These are characterized as being more forceful and lively than our Thoughts which are merely “copies of our impressions.”

How Impressions Become Thoughts

Impressions Become Thoughts through 4 Operations
Hume’s thinking on how Impressions become Thoughts through 4 operations

The material known to us through our five senses provide us with the material for knowledge. This material is then compounded (adding one to another), transposed (substitute a part of one thing with another), enlarged (made bigger) or diminished (made smaller) to form all the thoughts we have.

This Macat analysis does a great job explaining it.

How Thoughts Relate With Thoughts

Hume Thought Associations
Thoughts relate with Thoughts through 3 Associations

Sense impressions become copied into thoughts which undergo the four operations above. These thoughts are then set loose in the mind to form complex interactions that provide us with human understanding.

“The mind’s thoughts or ideas are obviously interconnected in some systematic way: there is some order and regularity in how, in memory and imagination, one idea leads to another.”

Hume traces back the strands of these complex thoughts and finds that they’re formed by one of three ways: resemblance, contiguity in space and time, and cause and effect.

Matters of Fact and Relations of Ideas

Matters of Fact use factual reasoning based upon experience. It deals in probabilities (like common truths) that are dependent upon “what exists and what is the case.” Whereas Relations of Ideas use demonstrative reasoning based upon pure thinking. It deals with certainties (like mathematical truths) that are independent of “what exists and what is the case.”


David Hume’s thinking “woke” Immanuel Kant from his “dogmatic slumber” and greatly influenced the development of Empiricism. Mix one-part Hume with Dorothy Sayer’s essay The Lost Tools of Learning and you’ll find yourself waking up from various slumbers.