Berkeley’s Human Knowledge

George Berkeley  A Treatise Concerning the Principles of Human Knowledge Part 1, London 1710

This has become infamous for an extreme version of ‘the observer effect’, but this may be a misunderstanding of what Berkeley meant. I have yet to read the full text, but his introduction seems to me to give some sensible advice on how to read his text, from which I agree with wikipedia that the ‘trees in forest’ view attributed to him may be misleading.


[When] we lay the blame for our paradoxes and difficulties on our faculties rather than on our wrong use of them, perhaps we are letting ourselves down too lightly.

It is hard to believe that right deductions from true principle should ever lead to conclusions that can’t be maintained or made consistent.

I deny that I can perform ‘abstraction’ in the standard meaning of that word, which covers two kinds of mental performance: (1) conceiving abstractly and in isolation a quality that couldn’t exist in isolation as we are said to do with colour and motion·; and (2) forming a general notion by abstracting from particulars in the way I have described, as we are said to do with man and animal·. There is reason to think that most people are like me in this respect. The majority of people, who are simple and illiterate, never claim to have abstract notions.

Suppose for example that a geometrician, proving the validity of a procedure for cutting a line in two equal parts, draws a black line one inch long. As used in this geometrical proof, this particular line is general in its significance because it is used to represent all particular lines, so that what is proved regarding it is proved to hold for all lines. And just as that particular line becomes general by being used as a sign, so the word ‘line’—which in itself is particular—is used as a sign with a general meaning. The line is general because it is the sign not of an abstract or general line but of all particular straight lines that could exist, and the word is general for the same reason—namely that it stands equally well for each and every particular line.

Who could believe that a couple of children cannot chatter about sugar-plums and toys until they have first tacked together numberless inconsistencies and so formed abstract general ideas in their minds, attaching them to every common name they make use of?

Abstract ideas are no more needed, in my opinion, for the growth of knowledge than they are for communication. I entirely agree with the widespread belief that all knowledge and demonstration concerns universal notions; but I can’t see that those are formed by abstraction. The only kind of universality that I can grasp doesn’t belong to anything’s intrinsic nature; a thing’s universality consists how it relates to the particulars that it signifies or represents.

[Although] the idea I have in view while I make the demonstration may be (for instance) that of an isosceles right-angled triangle whose sides are of a determinate length, I can still be certain that it applies also to all other triangles, no matter what their sort or size. I can be sure of this because neither the right angle nor the equality of sides nor length of the sides has any role in the demonstration.

So let us examine how words have helped to give rise to the mistaken view that there are abstract ideas.·… ·.(1) People assume that every name does or should have just one precise and settled signification.

It is one thing to make a name always obey the same definition, and another to make it always stand for the same idea: one is necessary, the other useless and impracticable.

(2) Words helped in another way to produce the doctrine of abstract ideas, namely through the widespread opinion that language is for the communicating of our ideas ..

It can’t be denied that words are extremely useful: they make it possible for all the knowledge that has been gained by the enquiries of men at many times and in all nations to be pulled together and surveyed by a single person. But at the same time it must be admitted that most branches of knowledge have been made enormously much darker and more difficult by the misuse of words and turns of phrase. Therefore, since words are so apt to influence our thoughts, when I want to consider any ideas I shall try to take them bare and naked, keeping out of my thoughts—as much as I can—the names that those ideas have been given through long and constant use. From this I expect to get the following·three·advantages:-

22 First, I shall be sure to keep clear of all purely verbal controversies. Secondly, this seems to be a sure way to extricate myself from that fine and delicate net of abstract ideas, which has so miserably perplexed and entangled the minds of men (with this special feature: the more sharp-witted and exploratory any man’s mind is, the more completely he is likely to be trapped and held by the net!). Thirdly, so long as I confine my thoughts to my own ideas with the words peeled off, I don’t see how I can easily be mistaken.

23 But I can’t get all these advantages unless I free myself entirely from the deception of words. I hardly dare promise myself that, because the union between words and ideas began early and has been strengthened by many years of habit·in thought and speech·, making it very difficult to dissolve. This difficulty seems to have been very much increased by the doctrine of abstraction. For so long as men thought their words have abstract ideas tied to them, it isn’t surprising that they used words in place of ideas: they found that they couldn’t set aside the word and retain the abstract idea in the mind, because abstract ideas are perfectly inconceivable.

24 But when you know that these are mistakes, you can more easily prevent your thoughts from being influenced by words. Someone who knows that he has only particular ideas won’t waste his time trying to conceive the abstract idea that goes with any name. And someone who knows that names don’t always stand for ideas will spare himself the labour of looking for ideas where there are none to be had.

25 Unless we take care to clear the first principlesof knowledge from being burdened and deluded by words,we can reason from them for ever without achieving any-thing; we can draw consequences from consequences and be never the wiser. The further we go, the more deeply and irrecoverably we shall be lost and entangled in difficulties and mistakes. To anyone who plans to read the following pages, therefore, I say: Make my words the occasion of your own thinking, and try to have the same sequence of thoughts in reading that I had in writing. This will make it easy foryou to discover the truth or falsity of what I say. You will run no risk of being deceived by my words, and I don’t see howyou can be led into an error by considering your own naked, undisguised ideas.

Main Body

First 50 sections

3. Everyone will agree that our thoughts, emotions, and ideas of the imagination exist only in the mind. It seems to me equally obvious that the various sensations or ideas that are imprinted on our senses cannot exist except in a mind that perceives them—no matter how they are blended or combined together (that is, no matter what objects they constitute). You can know this intuitively [= ‘you can see this as immediately self-evident’] by attending to what is meant by the term ‘exist’ when it is applied to perceptible things. The table that I am writing on exists, that is, I see and feel it; and if I were out of my study I would still say that it existed, meaning that if I were in my study I would perceive it, or that some other spirit actually does perceive it. …

4. It is indeed widely believed that all perceptible objects—houses, mountains, rivers, and so on—really exist independently of being perceived by the understanding. But however widely and confidently this belief may be held, anyone who has the courage to challenge it will—if I’m not mistaken—see that it involves an obvious contradiction. For what are houses, mountains, rivers etc. but things we perceive by sense? And what do we perceive besides our own ideas or sensations? And isn’t it plainly contradictory that these, either singly or in combination, should exist unperceived?

5. If we thoroughly examine this belief in things existing independently of the mind it will, perhaps, be found to depend basically on the doctrine of abstract ideas.

… To be convinced of this, you need only to reflect and try to separate in your own thoughts the existence of a perceptible thing from its being perceived—·you’ll find that you can’t·

8. ‘But’, you say, ‘though the ideas don’t exist outside the mind, still there may be things like them of which they are copies or resemblances, and these things may exist outside the mind in an unthinking substance.’ I answer that the only thing an idea can resemble is another idea; a colour or shape can’t be like anything but another colour or shape.

20. In short, if there were external bodies, we couldn’t possibly come to know this; and if there weren’t, we might havethe very same reasons to think there were that we have now. No-one can deny the following to be possible: A thinking being might, without the help of external bodies, be affected with the same series of sensations or ideas that you have,imprinted in the same order and with similar vividness in his mind. If that happened, wouldn’t that thinking being have all the reason to believe ‘There are corporeal substances thatare represented by my ideas and cause them in my mind’ that you can possibly have for believing the same thing? Of course he would; and that consideration is enough, all on its own, to make any reasonable person suspect the strength of whatever arguments he may think he has for the existence of bodies outside the mind.

23. ‘But’, you say, ‘surely there is nothing easier than to imagine trees in a park, for instance, or books on a shelf, with nobody there to perceive them.’ I reply that this is indeed easy to imagine; but let us look into what happens when you imagine it. You form in your mind certain ideas that you call ‘books’ and ‘trees’, and at the same time you omit to form the idea of anyone who might perceive them. But while you are doing this, you perceive or think of them! So your thought- experiment misses the point; it shows only that you have the power of imagining or forming ideas in your mind; but it doesn’t show that you can conceive it possible for the objects of your thought to exist outside the mind. To show that, you would have to conceive them existing unconceived or unthought-of, which is an obvious contradiction. However hard we try to conceive the existence of external bodies, all we achieve is to contemplate our own ideas.

35. I don’t argue against the existence of any one thing that we can take in, either by sense or reflection. I don’t in the least question that the things I see with my eyes and touch with my hands do exist, really exist. The only thing whose existence I deny is what philosophers call ‘matter’ or ‘corpo-real substance’. And in denying this I do no harm to the rest of mankind—·that is, to people other than philosophers·—because they will never miss it. The atheist indeed will lose the rhetorical help he gets from an empty name, ‘matter’, which he uses to support his impiety; and the philosophers may find that they have lost a great opportunity for word-spinning and disputation.

36. If you think that this detracts from the existence or reality of things, you are very far from understanding what I have said in the plainest way I could think of.

Much of the above seems uncontroversial and logical in the modern sense, and we can easily follow Locke’s advice in making some sense of the rest for ourselves, without necessarily claiming to have much insight not what Berkeley actually thought. He is critiquing a narrowly mechanistic and deterministic view of life and seems to be ‘creating space’ for the possible existence of ‘spirits’. Fair enough.

Second 50 sections

I haven’t quoted from any of this. Sometimes Berkeley seems to use the term ‘spirit’ to simply mean anthing that can affect an idea that is not itself an idea, such as a ‘thinking being’. At other times he seems to be showing signs of his journey to becoming a Bishop. So I take Locke’s advice and for now only comment that I have failed to make much sense of it.

Final Sections

Berkeley considers the implications of his views, which (perhaps fortunately) dont much depend on how we (or he) conceive of ‘spirits’. In particular, while the previous sections seem (on a quick scan) to suggest something like ‘As long as we follow God’s will we can develop sciences in ways which will meet with his approval and hence be beneficial’, we can ignore this suggestion and still make sense of his conclusions.

107. … by diligently observing the phenomena within our view, we can discover the general laws of nature, and from them deduce further phenomena. I don’t say demonstrate [= ‘prove in a rigorously valid manner’]; for all deductions of this kind depend on supposing that the author of nature always operates uniformly, constantly keeping to those rules that we regard as principles—though we can’t know for sure that they are.

(This distinction between ‘deduce’ and ‘demonstrate’ seems vital.)

108. Those men who make general rules from phenomena, and afterwards derive phenomena from those rules, seem to be considering signs rather than causes. A man may understand natural signs well without being able to say bywhat rule a one .event is a sign of another. And just as it ispossible to write improperly through too strictly observing general rules of grammar, so also in arguing from general rules of nature we may extend the analogy too far and thus run into mistakes.

110. The best key to natural science is widely agreed to be a certain celebrated treatise of mechanics—·Newton’s Principia·. At the start of that justly admired treatise, time, space, and motion are each distinguished into absolute and relative,·or, giving the same distinction in different words·,true and apparent, or·in yet other words·mathematical and vulgar [= ‘that of the plain uneducated ordinary person’]. According to the author’s extensive account of it, this distinction does presuppose that time, space and motion exist outside the mind, and that they are ordinarily•conceived as relating to perceptible things; but really in their own nature they have no relation to them at all.

112. Despite all this, it doesn’t appear to me that there can be any motion except relative motion. To conceive motion,·it seems to me·, one must conceive at least two bodies that alter in their distance from, or position in relation to, each other. Hence if there was one only body in existence, it couldn’t possibly be moved. This seems obvious, because the idea that I have of motion necessarily includes relation.

116. From what has been said, it follows that the scientific consideration of motion doesn’t imply the existence of an absolute space, distinct from the space that is perceived by the senses, is related to bodies, and cannot exist outside the mind, as is clear from the principles that prove the samething of all other objects of sense. If we look into it closely we shall perhaps find that we can’t even form an idea of pure space without bodies. This, I must confess, seems impossible, as being a most abstract idea.

118. Up to here I have written about natural science. Now letus enquire into that other great branch of speculative knowledge, namely mathematics. See the start of 101·.Celebrated though it is for its clearness and certainty of demonstration, which is matched hardly anywhere else, mathematics cannot be supposed altogether free from mistakes if in its principles there lurks some secret error that mathematicians share with the rest of mankind. Mathematicians deduce their theorems from premises that are highly certain; but their first principles are confined to the concept of quantity; and they don’t ascend into any enquiry concerning those higher maxims that influence all the particular sciences including ones that aren’t quantitative·. Any errors involved in those higher maxims will infect every branch of knowledge, including mathematics. I don’t deny that the principles laid down by mathematicians are true, or that their methods of deduction from those principles are clear and beyond dispute. But I hold that there are certain erroneous maxims that spread wider than mathematics, and for that reason are not explicitly mentioned there, though they are tacitly assumed throughout the whole progress of that science; and that the bad effects of those secret, unexamined errors are diffused through all the branches of mathematics. To be plain, I suspect that mathematicians as well as other men are caught in the errors arising from the doctrines of abstract general ideas and of the existence of objects outside the mind.

119. Arithmetic has been thought to have for its object abstract ideas of number. A considerable part of speculative knowledge is supposed to consist in understanding the properties and mutual relations of numbers. The belief in the pure and intellectual nature of numbers in the abstract has won for them the esteem of those thinkers who put on a show of having an uncommon subtlety and elevation of thought. It has put a price on the most trifling numerical theorems that are of no practical use and serve only to pass the time; and it has infected the minds of some people so much that they have dreamed of mighty mysteries involved in numbers, and tried to explain natural things by means of them. But if we look into our own thoughts, and consider the doctrines I have laid down, we may come to have a low opinion of those high flights and abstractions, and to look on all researches into numbers as mere earnest trivialities insofar as they aren’t practically useful in improving our lives.

122. In arithmetic therefore we have to do not with the things but with the signs, though these concern us not for their own sake but because they direct us how to act in relation to things, and how to manage them correctly. Just as I have remarked concerning language in general (19 intro), so here oo abstract ideas are thought to be signified by numerals or number-words at times when they don’t suggest ideas of particular things to our minds. I shan’t go further into this subject now, except to remark that what I have said shows clearly that the things that are taken to be abstract truths and theorems concerning numbers are really about nothing but particular countable things—or about names and numerals, which were first attended to only because they are signs that can aptly represent whatever particular things men needed to calculate about. To study these names or numerals for their own sake, therefore, would be just as wise and pointful as to neglect the true use or original intention and purpose of language, and to spend one’s time on irrelevant criticisms of words, or on purely verbal reasonings and controversies.

123. From numbers we move on to discuss extension, which (considered as relative) is the object of geometry. The infinite divisibility of finite extension, though it isn’t explicitly asserted either as an axiom or as a theorem in the elements of geometry, is assumed throughout it, and is thought to have so inseparable and essential a connection with the principles and proofs in geometry that mathematicians never call it into question. This notion is the source of all those deceitful geometrical paradoxes that so directly contradict the plain common sense of mankind, and are found hard to swallow by anyone whose mind is not yet perverted by learning. It is also the principal source of all the fine-grained and exaggerated subtlety that makes the study of mathematics so difficult and tedious. So if I can make it appear that nothing whose extent is finite contains innumerable parts, or is infinitely divisible, that will immediately free the science of geometry from a great number of difficulties and contradictions that have always been thought a reproach to human reason, and also make the learning of geometry a much less lengthy and difficult business than it has been until now.

126. I have pointed out that the theorems and demonstrations of geometry are about universal ideas (15 intro). And I explained in what sense this ought to be understood, namely that the particular lines and figures included in the diagram are supposed to stand for innumerable others of different sizes. In other words, when the geometer thinks about them he abstracts from their size; this doesn’t imply that he forms an abstract idea, only that he doesn’t care what the particular size is, regarding that as irrelevant to the demonstration.

132. It may be said that various undoubtedly true theorems have been discovered by methods in which infinitesimals were used, which couldn’t have happened if their existence included a contradiction in it. I answer that when you look into this thoroughly you won’t find any case where you need to conceive infinitesimal parts of finite lines, or even quantities smaller than the smallest you can perceive. You’ll find that this is never done, because it is impossible. This completes my discussion of infinite divisibility.


Locke’s Ideas


Berkeley is critiquing John Locke’s An Essay Concerning Human Understanding, in particular the somewhat quaint view that our perceptions ‘directly’ correspond to some real ‘thing’. Given Locke’s “Substances are “nothing but the assumption of an unknown support for a group of qualities that produce simple ideas in us”, I’m not sure if Berkeley applied the idea in his last paragraph above to his reading of Locke, but maybe that doesn’t matter?


Berkeley makes a critical distinction between a deduction from one’s ideas about a topic, and a demonstration of the validity of the deduction. (Economists take note!) I would have to re-read Locke to see if he gets this. (Newton did?)


Berkeley’s first publication was in mathematics, and he went on to write his ‘Analyst’, that led to a process of reform that can be traced until at least 1966, and which may not be complete. (I hope it is!) It might therefore be reasonable to read that to clarify any issues.

[Wikipedia] opines:

“The logical criticism is that of a fallacia suppositionis, which means gaining points in an argument by means of one assumption and, while keeping those points, concluding the argument with a contradictory assumption.” “Berkeley, however, found it paradoxical that “Mathematicians should deduce true Propositions from false Principles, be right in Conclusion, and yet err in the Premises.”

Berkeley was himself a mathematician, whereas Locke was not, and it is not clear to me that Berkeley was criticising mathematicians as such, rather than Locke’s understanding of mathematics. In any case, mathematics has moved on, and there seems no reason to think that the above comment would apply today.

(Berkeley is particularly critical of the characterisation of arithmetic, geometry and calculus as being about abstarctions from physical ‘reality’ as then conceived. He advocated  a formal approach to number, and a relativistic and finitistic approach to space and time.)


Locke writes about abstraction by analogy with his view of mathematical reasoning. Berkeley makes a similar analogy, but this results in a more refined view of methods that had been thought of in terms of ‘abstraction’.


I am not quite clear that contemporary psychologists quite get Berkeley’s point, but I haven’t come across any evidence to the contrary, centuries later. Kahneman, for example, opines:

System 1 represents categories by a prototype or a set of typical examples.

I’m not sure this actually true, but it is at least consistent with Berkeley: no abstraction as such.


Some psychologists use computers as a metaphor for human cognition. Computers can go beyond what Kahneman supposes, above, in the sophistication of their representations (and typically do), but many contemporary psychologist’s views would still seem consistent with Berkeley.

The main essay

Wikipedia opines:

This theory denies the existence of material substance  .. His arguments were a precursor to the views of Mach and Einstein. …Interest in Berkeley’s work increased after World War II because he tackled many of the issues of paramount interest to philosophy in the 20th century.

George Berkeley’s theory that matter does not exist comes from the belief that “sensible things are those only which are immediately perceived by sense”. The only causes that exist in Berkeley’s worldview are those that are a result of the use of the will.

But an alternative reading seems to be that there may be a reality that remains that would be perceived as a tree if we looked: it is simply that the reality could be beyond our powers of perception, and so nothing like ‘a tree’ as we perceive it.

Russell ( A History of Western Philosophy and Its Connection with Political and Social Circumstances from the Earliest Times to the Present Day) has some important technical criticisms of Berkeley’s logic, showing that logicians had made progress in the centuries since Berkeley.

One could argue that Berkeley still seems ‘essentially correct’ and he seems much more accessible than anything from the last 100 years. (But maybe that’s not saying much!)

An interpretation

The following scholastic beliefs were once widespread:

  • That words stand for ideas, particularly abstract ideas, that can be communicated.
  • That every name does or should have just one precise and settled signification.
  • That science and mathematics, for example, depends on abstract ideas, such as ‘point’ and ‘line’.

If true, they would seem to suggest that it would, at least in principle, be possible for science to establish empirical ‘facts’. That would be convenient.

From a contemporary viewpoint, Berkeley’s objections seem reasonable. For example, current SATNAV’s are very good at reasoning about their maps, which is often adequate for our purposes, but sometimes they would do better for us if they somehow could reason about actual roads, or at least roads as we perceive them. ‘The map is not the territory‘.

No-one has been able to explain what possible real processes might bring about such fortunate circumstances, or how we could know that they had, even if they did. They seem to need either inherited ‘innate ideas’, ESP or at least one ‘god’. For example, it is not at all clear how computers might become ‘intelligent’ to take account of the limitations of their internal representations and demonstrate what Keates called ‘negative capabilties‘. Yet controversy seems to linger. Perhaps we would could simply agree that even if these beliefs might be true, we could never be absolutely sure about them in particular circumstances. There is always some irreducible uncertainty, even if we don’t realise it, and no matter how ‘pragmatic‘ we think we are or how authoritative we wish to appear.

Dave Marsay

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