Outline of Hume’s Theory of Knowledge

This is an outline of his main points. A Table of main points at the end. Post is great for students in Phil. 101 and other interested readers.

Epistemology is the study of how we acquire knowledge. What is the “foundation” of science? What is the difference between a priori knowledge and a posteriori knowledge?

Let’s begin.

I. Perception of the Mind

A. Thoughts or ideas

1. Less forcible and less vivacious (living)

B. Impressions

1. Lively perceptions

C. Imagination

1. Compounding, transposing, augmenting, or diminishing material

a. For example, gold + mountain = golden mountain

b. For example, virtue + horse = virtuous horse

2. What about God?

a. Goodness and wisdom + a human + infinite degree = God.

b. So God is a product of our imagination.

II. Human Reasoning

A. Relation of ideas

1. Intuitive (“secure” form of acquiring knowledge)

a. In classical epistemology the word means “taking in” as in seeing white paper, or a circle is different from a square, or sun hurts my eyes when I look at it.

2. Demonstrative (involves an extra step)

a. For example, Square of hypotenuse is equal to squares of the two sides

b. For example, Three times five is half of thirty

c. No need of empirical existence of these things, but discoverable by reason alone; e.g. No need for a perfect circle to exist in nature, but calculations can be made.

B. Matters of Fact

1.. Usually physical, empirical events

2. No logical contradiction in nature

3. For example:

(a) The sun will not rise tomorrow

(b) The sun will rise

4. Reasoning about Matter of Fact are founded on relation of cause and effect

5. For example:

a. We believe friend is in France. Why? (See III)

b. We see a watch or machine on a deserted island, so we infer a human was there. Why? (See III)

c. Hearing voice and discourse in darkness, we infer there was a human. Why? (See III)

III. Cause and Effect

A. Discoverable, how?

1.. Not by reason [alone] (a priori)

2. But by experience (five senses) (a posteriori)

3. For example, a marble slab is just sitting there. How do you know:

a. Breaking it one way requires great force but in another way hardly any force?

c. Answer: By experience! Not by reason [alone]! You experiment with marble

4. For example, explosion of gunpowder and attraction of magnet.

a. How do you know that if they were just sitting there? By experience, not by reason [alone]!

5. For example, how do you know bread and egg properly nourish humans, but not lions and tigers (and bears!)

a. By experience, not by reason (a priori) alone!

6. For example, we’re brought into this planet “of a sudden” and we see a cue ball. How would we know it would cause another to move?

a. By experience, not by reason [alone]!

IV. Three Questions

A. What is nature of all reasoning about Matter of Fact?

1.. Relation of cause and effect

B. What is foundation of reasoning and concluding about that relation?

1.. Experience (a posteriori)

C. What is foundation of all conclusions about Experience?

1.. That’s the quest Hume is on

D. Similarity

1.. “From causes that appear similar we expect similar effects”

2. That is sum of all conclusions from Experience

3. Cause is conjoined to effect, and vice-versa

E. If it were reason [alone] (a priori) . . .

1.. . . . We could conclude just by looking at an egg for first time that it would nourish us

2. Same goes for bread

3. But it’s not intuitive or demonstrative

4. No process of logic, but experience

F. What is foundation of all conclusions about Experience?

1.. Custom or habit!

2. Ta-Da! Nothing more!

G. Hume is an Empiricist!


Hume says the foundation of our experience of the world is simple custom or habit.

Therefore, cause / effect is not conjoined logically, but we perceive it is conjoined by simple custom, not by a priori reasoning.

Custom or habit is a posteriori (in the right column, below)


Hume is an empiricist, and some consider him a skeptic (he would call himself an academic skeptic).

Hierarchy / Foundation:

4. Matters of Fact

3. Cause and Effect

2. Experience

1. Custom or Habit

Conclusion: Custom or Habit is a weak foundation for the world of empirical data (e.g. science). It is much weaker than Intuitive Knowledge (e.g. we can see sun is in sky) or Demonstrative Knowledge (we can demonstrate math)

Foundation of our knowledge of Matters of Fact is our idea of cause / effect.

Foundation of our knowledge of our idea of cause / effect is our experience.

Foundation of our experience with the outside world is uniformity or regularity in nature (which is based on uniformity or regularity of cause/effect.)

Thus, our reliance on #3 is based on #1, and our reliance on #1 is based on #3, which is circular.

However, there is no logical contradiction in this statement: bread will not nourish us.

Quick Summary


A Priori

A Posteriori

Knowledge without reference to or dependence on experiencing world Knowledge that comes from experiencing world

(Empiricism = Experience)

Relations of Ideas Matters of Fact
Intuitive Knowledge;

Demonstrative Knowledge

Experience of cause/effect Custom or habit
Examples: Geometry, Arithmetic, Algebra, Laws of Logic Examples: Natural world around us, e.g., the sun coming up tomorrow, bread and egg nourishing humans; billiard ball striking another one and moving it
Impossible to find a logical contradiction, e.g., it is logically impossible that a triangle would not have three sides or that three times five would not equal half of thirty There is no logical contradiction in these statements: the sun will not come up; sun will come up. Besides, in some cases cause / effect actually breaks down
Reasoning and process of thought in our mind alone (though we may have to check our proofs on paper or see a triangle) Impressions from outside world, which we process afterwards in our mind


Hume’s Argument against Design

ARTICLES IN OUTLINE SERIES (alphabetical order)

Aristotle’s Virtue Ethics

Clifford’s Ethics of Belief

Descartes’s Mind-Body Separation (Meditations I and II)

Hick’s Evil and God of Love

Hume’s Argument against Design

Hume’s Theory of Knowledge

James’s Will to Believe

Kant’s Ethics

Locke’s Theory of Knowledge

Mill’s Utilitarian Ethics

Nietzsche’s “Death of God”

Paley’s Watchmaker Design Argument

Plato’s View of Justice and the Soul

Plato the Soul Man

Rachels’s Moral Objectivism

Ryle’s Category Mistake

Sartre’s “Existentialism and Humanism”

Socrates’s “Apology”

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