QuestionsIs the world real?The mind has only its perceptions: the external world cannot be proved
Is the world real?No way to know

The mind has only its perceptions: the external world cannot be proved

Hume's scepticism about the external world; the veil of perception

David Hume 1711 · 1776Neither causation nor induction can be proved: custom guides us.
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What it claims

No reasoning proves the existence of external objects, and our belief in them comes from instinct, not from reason.

Why

We cannot compare a perception with an object we never perceive: so no experience links our perceptions to the world.

In short

"The mind has only its perceptions: the external world cannot be proved" is an argument by David Hume (Enquiry concerning Human Understanding, XII, part 1 (1748)) on the question "Is the world real?" (answer: no way to know). Its claim: No reasoning proves the existence of external objects, and our belief in them comes from instinct, not from reason. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P4). AskPhilosophy presents 3 objections, 0 of them with a documented reply, and the original text behind each premise, checked word for word.

Enquiry concerning Human Understanding, XII, part 1 (1748)
Valid with an implicit premise

Everyone believes the table we see exists even when nobody looks at it. Hume notes that this belief comes from an instinct, before any reasoning. But the slightest reflection makes trouble for it: the table seems to shrink as we move away, yet the real table does not change; so what the mind has before it is only an image. Now, if we never have before the mind anything but perceptions, how can we know that they come from external objects that resemble them? Hume answers that no experience and no reasoning proves it. He does not say we should stop believing in the world; he says this belief rests on nature, not on reason.

P1Nothing is ever present to the mind but its perceptions. So it can never compare a perception with an external object, nor have any experience of their connexion.
P2Whether our perceptions are produced by similar external objects is a question of fact, which can only be settled by experience: one would have to be able to compare.
P3No a priori reasoning proves either that perceptions must come from external objects: they could come from the mind itself, from an invisible spirit, or from a cause still more unknown.
P4 · implicit premiseOnly experience or reasoning could establish the existence of external objects as causes of our perceptions.
P5Yet men believe in the external world by a natural instinct, almost before the use of reason.
Therefore no reasoning proves the existence of external objects, and our belief in them comes from instinct, not from reason.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P4, the computer finds a case where neither experience nor a priori reasoning proves the external world, and yet it is proved in another way, for instance by a proof of a third kind.
The argument is valid with the hidden premise P4. If perceptions and objects cannot be compared (P1), experience can establish nothing (P2); reasoning alone cannot either (P3); and since only one or the other could do it (P4), the existence of the external world is not proved. With P5, instinct is the only source of the belief. Objections target P1 (the theory of perceptions) and P3 (the simplicity of the world hypothesis).
Analogy. A prisoner has seen the world only in photographs. He cannot check that they resemble what they show: to compare a photo with the thing, he would have to get out. Hume says our mind is that prisoner, with no door.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Thomas Reid 1764 · attacks premise 1

Reid finds Hume's reasoning just, given its principles. But he refuses the conclusion: so those principles, inherited from Locke and Descartes, must be questioned, in particular the idea that we perceive only our ideas. For him, we perceive things directly.

no reply
We have not yet found a direct reply by Hume in the texts.
The debate goes on (our summary) Our summary: Hume did not answer Reid on the substance; in 1775, an advertisement added to his Essays only asks that his philosophy be judged by the Enquiry, not by the youthful Treatise his critics attacked. A defender of Hume would say that refusing a premise is not refuting it, and would point to the shrinking table (EHU XII, 9), which shows that what we see varies while the object does not change.
Where the debate stands (our summary)Our summary: the debate between direct realism and the theory of intermediate perceptions is still open in the philosophy of perception.
Bertrand Russell 1912 · attacks premise 3

Russell grants Hume that the external world cannot be proved. But the hypothesis that life is only a dream, though not logically contradictory, is a less simple way of accounting for the facts than the common-sense hypothesis: objects independent of us whose action causes our sensations.

no reply
see the argument
No reply possible: objection raised in 1912, after the author's death (1776).
The debate goes on (our summary) Our summary: Hume could not answer Russell, who came about a hundred and sixty years later. A defender of Hume would say that calling a hypothesis "simpler" already assumes links between perceptions that experience alone does not guarantee.
Where the debate stands (our summary)Our summary: many philosophers accept the idea of "best explanation"; others ask why simplicity should be a sign of truth.
G. E. Moore 1939 · attacks the conclusion

Moore maintains that he knows that here is a hand, and that it would be absurd to say he only believes it. This certainty is stronger than any sceptical premise: if Hume's argument proved he does not know, it is the argument that would have to be rejected.

no reply
see the argument
No reply possible: objection raised in 1939, after the author's death (1776).
The debate goes on (our summary) Our summary: Hume could not answer Moore. His position is nevertheless close: he admits we cannot stop believing in the world, for "nature has not left this to our choice"; he only refuses to call this belief knowledge proved by reason.
Where the debate stands (our summary)Our summary: Moore and Hume agree on the fact of believing and differ on what reason can justify. An open point.