QuestionsIs the world real?To be is to be perceived: there is no matter
Is the world real?It is all in the mind

To be is to be perceived: there is no matter

Berkeley's immaterialism; esse est percipi; subjective idealism; matter does not exist

George Berkeley 1685 · 1753Sensible things exist only by being perceived: there is no matter behind our ideas, only minds.
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What it claims

There is no matter: sensible things exist only in minds, and those that nobody perceives subsist in the eternal mind of God.

Why

We perceive only our own ideas, and an idea exists only in a mind; nothing outside a mind can resemble them.

The same idea through history
John Locke1689Locke distinguishes primary qualities (extension, shape, motion), which would resemble things, from secondary qualities (colours, sounds, tastes), which would not. Berkeley starts from this distinction and turns it around: if the second exist only in the mind, so do the first.
George Berkeley1710§ 9 of the Principles: the very notion of "matter", a thoughtless substance in which extension and motion would subsist, would be contradictory. Three years later, the Three Dialogues between Hylas and Philonous take up the thesis in conversation form.
Vasubandhu400A comparison, with no historical link: some thirteen centuries earlier, in India, Vasubandhu holds that what we perceive is only representation, with no external object. They part ways on one point: Berkeley relies on an eternal mind that perceives everything, Vasubandhu on a stream of representations whose causes lie in consciousness itself.
In short

"To be is to be perceived: there is no matter" is an argument by George Berkeley (Berkeley, Principles of Human Knowledge, 1710, § 1-9; Three Dialogues, 1713, 1710) on the question "Is the world real?" (answer: it is all in the mind). Its claim: There is no matter: sensible things exist only in minds, and those that nobody perceives subsist in the eternal mind of God. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P4, P5, P6). AskPhilosophy presents 3 objections, 1 of them with a documented reply, and the original text behind each premise, checked word for word.

Berkeley, Principles of Human Knowledge, 1710, § 1-9; Three Dialogues, 1713
Valid with an implicit premise

You put your cup on the table and leave the room. Does it still exist? Almost everyone says yes. Berkeley, a 25-year-old Irish philosopher in 1710 (he would become a bishop later), answers in a surprising way: a sensible thing is nothing but what we perceive of it (its colour, hardness, weight). Now perceiving means having ideas, and ideas exist only in a mind. So behind our perceptions there is no "matter" that would exist all by itself. Careful: Berkeley does not say the world is an illusion. He says the cup is perfectly real, but made of ideas, and that these ideas do not stop existing when you close your eyes, because God always perceives them. He thought he was defending common sense and religion against scepticism and atheism.

P1Sensible things (houses, mountains, rivers) are what we perceive by the senses; and we perceive by the senses only our own ideas or sensations.
P2An idea or sensation can exist only in a mind that perceives it: one cannot separate, even in thought, a sensible thing from its being perceived.
P3An idea can be like nothing but an idea. If it is said that there exist outside the mind things that resemble our ideas, these originals are either perceivable (then they are ideas) or not perceivable (and a colour cannot be like something invisible).
P4 · implicit premiseThe philosophers' "matter" is what is supposed to exist outside every mind, as the original of which our ideas of extension, shape and motion would be copies.
P5 · implicit premiseSensible things also exist when no human mind perceives them: the mountain does not vanish when nobody looks at it.
P6 · implicit premiseWhat exists only in a mind, and yet exists when no created mind perceives it, exists in the mind of an eternal spirit.
Therefore there is no matter: sensible things exist only in minds, and those that nobody perceives subsist in the eternal mind of God.

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, one could grant that our ideas resemble nothing external, and yet believe that there exist things outside us that cause them, without resembling them. The argument does not rule this out without P4, nor without a reply from Berkeley (§ 18-20) saying that we have no reason to believe it.
The argument is valid. P1 and P2 give: sensible things exist only in a mind. P3 and P4 give: matter cannot exist (it would be both outside every mind and like ideas, which are in the mind). P5 and P6 explain why the world does not vanish: it is perceived by God. P4, P5 and P6 are premises Berkeley assumes; they were added out of charity.
Analogy. At the cinema, you see a coloured image on the screen: it exists only for eyes that look at it. Berkeley says the same of the table, the cup, the mountains. If nobody is looking, there is still the projector: for Berkeley, that is God.

Objections

3

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

Samuel Johnson 1763 · attacks the conclusion

One day in 1763, James Boswell tells Samuel Johnson that Berkeley's doctrine cannot be refuted, though we are sure it is false. Johnson then strikes his foot with mighty force against a large stone, rebounds from it, and answers: "I refute it thus." For him, the hardness of the stone proves that it exists outside us.

Berkeley replies
George Berkeley 1710 · 1710 text, written before the objection (reply to a similar objection)
Berkeley foresees this objection. He says he does not argue against the existence of any thing we grasp by sense or reflection: that the things I see and touch exist, he does not doubt in the least. The only thing whose existence he denies is what philosophers call matter. The shock of the stone is therefore quite real: it is a sensation of touch, an idea in a mind.
The debate goes on (our summary) The debate goes on (our summary). It is often said that Johnson's kick misses the thesis, since Berkeley grants that the stone is hard: the question is what this hardness is (an idea, or a property of matter). Johnson's gesture is above all famous as a symbol of the appeal to common sense.
Where the debate stands (our summary)Underlying point: common sense and Berkeley agree on what we feel (the stone is hard), and differ on what it is (an idea in a mind, or a property of a thing outside every mind). The kick does not settle this disagreement.
George Edward Moore 1903 · attacks premise 2

In "The Refutation of Idealism", Moore attacks the formula esse est percipi and aims to show that it is false in every sense given to it. He distinguishes in every sensation the act of awareness and what one is aware of. When I see blue, the blue is the object of my experience, not a mere content of my mind: it is as independent as any real thing. To have a sensation is already to be outside the "circle of our ideas".

no reply
No reply possible: objection raised in 1903, after the author's death (1753).
The debate goes on (our summary) The debate goes on (our summary). Moore mainly aims to show that the argument leading from "perceived" to "exists only in the mind" rests on a confusion between the act of perceiving and the thing perceived. We have no text by a defender of Berkeley answering Moore to quote here.
Where the debate stands (our summary)Underlying point: does the sensation of blue contain two elements (an act and an object), or only one? Moore says two, Berkeley one.
David Hume 1748 · attacks the conclusion

Hume, in a note to the Enquiry concerning Human Understanding, judges that most of Berkeley's writings form the best lessons of scepticism. Berkeley says he wrote against the sceptics, but his arguments, according to Hume, are in reality sceptical: they admit of no answer and produce no conviction. Their only effect is a momentary amazement and confusion.

no reply
We have not yet found a direct reply by Berkeley in the texts.
The debate goes on (our summary) The debate goes on (our summary). Berkeley saw himself as an enemy of scepticism, since he thought he gave the world back its reality by denying only matter. Hume judges on the contrary that his argument, taken seriously, pulls the ground from under everyone, without anyone believing it. Berkeley did not, in our texts, answer this note.
What today's voices say
Defend it
Donald HoffmanHe says there is a lot in common with Berkeley, but he avoids the word idealism because it is often tied to anti-science and anti-realism. He wants a mathematically precise, testable theory of a real network of conscious agents.