Skepticism About the External World

Where it surfaces

• Section VI: Of Modes and Substances

  By reducing substance to a collection of qualities, Hume undermines the notion of an unknown substratum, a key skeptical move.

• Part II: Of the Ideas of Space and Time

  The rejection of the idea of a vacuum and the limitation of our ideas to what is derived from impressions demonstrates a skeptical stance towards concepts that go beyond our perceptual experience.

• Section I: Of the Infinite Divisibility of Our Ideas of Space and Time

  Hume challenges common assumptions about the nature of objects, suggesting that our perceptions may not accurately represent their true divisibility.

• Section II: Of the Infinite Divisibility of Space and Time

  By questioning the infinite divisibility of space and time, Hume challenges the nature of external reality and our ability to know it.

• Section III: Of the Other Qualities of Our Idea of Space and Time

  Hume's analysis reduces space and time to mere collections of perceptions, challenging the notion of an independent external reality.

• Section IV: Objections Answered

  Hume questions the certainty of geometrical and mathematical knowledge, suggesting that our standards of equality and perfection are imaginary fictions.

• Section V: The Same Subject Continued

  Hume confesses that he cannot penetrate into the nature of bodies, only knowing their external properties as they affect the senses.

• Section VI: Of the Idea of Existence, and of External Existence

  Hume argues that we cannot conceive of external objects as specifically different from our perceptions, and that our idea of them is only relative, undermining the common notion of an independent external world.

• Section I: Of Knowledge

  Hume's critique of geometry and the limits of certainty in knowledge reflects a skeptical stance toward claims that go beyond what is given in impressions.

• Section II: Of Probability, and of the Idea of Cause and Effect

  Hume argues that causation is the only relation that goes beyond the senses, yet he questions our ability to know necessary connections, leading to skeptical conclusions about our knowledge of external objects.

• Section III: Why a Cause Is Always Necessary

  Hume questions the intuitive certainty of the causal principle, suggesting that our belief in causality is not grounded in reason but in custom and experience.

• Section IV: Of the Component Parts of Our Reasonings Concerning Cause and Effect

  The section implies that without impressions, our reasoning about causes and effects is chimerical, highlighting the limits of knowledge.

• Section IX: Of the Effects of Other Relations and Other Habits

  The discussion of how we form a system of realities from memory and senses, and another from judgment, touches on the nature of our beliefs about existence beyond immediate perception.

• Section X: Of the Influence of Belief

  Hume's distinction between the force of belief and the weaker fictions of poetry underscores his skeptical view that our convictions are based on custom rather than rational certainty.

• Section XI: Of the Probability of Chances

  Hume's analysis of chance and probability underscores the limits of human knowledge, as we cannot have certainty about future events, only probabilistic expectations.

• Section XII: Of the Probability of Causes

  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.

• Section XIII: Of Unphilosophical Probability

  The chapter highlights contradictions in human reason, showing how general rules can subvert and then save philosophy, reinforcing skeptical doubts about the foundations of knowledge.

• Section XVI: Of the Reason of Animals

  Hume notes that beasts never perceive any real connection among objects, and that their inferences are based on experience, not on any rational insight into necessary connections.

• Part IV: Of the Sceptical and Other Systems of Philosophy

  Hume questions the evidence for the existence of external objects and the nature of our belief in them.

• Section I: Of Scepticism with Regard to Reason

  Hume extends skepticism to reason itself, arguing that all knowledge reduces to probability, undermining certainty in demonstrative sciences.

• Section II: Of Scepticism with Regard to the Senses

  Hume argues that the senses cannot give us a notion of continued or distinct existence, and that the belief in external objects is a product of the imagination, not reason.

• Section III: Of the Ancient Philosophy

  Hume questions the notion of substance and identity, arguing that our belief in a continuous external world is a fiction of the imagination.

• Section IV: Of the Modern Philosophy

  Hume argues that the modern philosophy's principles lead to a total annihilation of external objects, leaving no just idea of solidity or matter, thus resulting in extravagant skepticism.

• Section V: Of the Immateriality of the Soul

  Hume extends skepticism to the nature of the mind, questioning the very meaning of substance and inhesion, and showing that the question of the soul's immateriality is unintelligible.

• Section VI: Of Personal Identity

  Hume's skepticism extends to the self, as he denies any real bond among perceptions and suggests that identity is a quality we attribute due to the imagination.

• Section VII: Conclusion of This Book

  Hume expresses profound doubt about the ability of reason to justify our beliefs, noting that even after accurate reasoning, he can give no reason for his assent, only a strong propensity to view objects in a certain way.

• Section I: Of Liberty and Necessity

  Hume emphasizes that we cannot penetrate the essence of bodies to discover necessary connections; we only observe constant conjunction, leading to a skeptical view of causal necessity.

• Section I: Moral Distinctions Not Derived from Reason

  Hume's skepticism about reason's ability to discover moral relations parallels his broader skepticism about causal connections and external objects.

• Section IV: Of the Transference of Property by Consent

  Hume's skepticism about the real nature of property, which he calls 'insensible and inconceivable,' leads to the need for symbolic aids.

• Appendix

  Hume's confession of being in a labyrinth and his plea for scepticism highlight the limits of human understanding.

• Endnotes

  Hume advocates a modest skepticism regarding the real nature of objects and distances, suggesting that our knowledge is limited to appearances.