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Summary: A Treatise Concerning the Principles of Human Knowledge

The Principles of Human Knowledge were written by the Irish bishop George Berkeley in 1710, and their main aim was to respond to the impious doctrines of materialism and atheism. To this end, he develops a surprising theory of knowledge, based on radical empiricism: ‘to be is to be perceived’.


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Berkeley, an Irish bishop, wrote this work for skeptics and unbelievers.


It is often the use of our thinking which, raising on a given subject various problems, leads to scepticism. This is due not to reason itself, but to the misuse we make of it. Hence this famous metaphor:

The far greater Part, if not all, of those Difficulties which have [...] block’d up the way to Knowledge, are intirely owing to our selves. [...] We have first rais’d a Dust, and then complain, we cannot see 1.


So what are these false principles that we have followed and that have lost us?

It concerns the notion of abstraction, and by extension abstract ideas. These are in fact considered to be the objects of logic or metaphysics, whereas they are merely fictions. Or again: we have no abstract ideas.


Berkeley sums up the doctrine of abstraction as follows:

Qualities [...] do never really exist each of them apart by it self, and separated from all others, but are mix’d [...] and blended together, several in the same Object. But we are told, the Mind being able to consider each Quality singly, or abstracted from those other Qualities with which it is united, does by that means frame to it self abstract Ideas. 2.

Berkeley takes an example: if one sees an an Object extended, coloured, and moved, the mind distinguishes this compound object into simple ideas, and does frame the abstract Ideas of Extension, Colour, and Motion 3. He specifies: Not that it is possible for Colour or Motion to exist without Extension: but only that the Mind can frame to it self by Abstraction the Idea of Colour exclusive of Extension 4.

The abstract idea would be a general idea grouping together what is common to the things of which it is the idea.

Another example shows the astonishing character of this doctrine: it makes an Idea of Colour in abstract which is neither Red, nor Blue, nor White, nor any other determinate Colour. 5.

Abstract ideas would be forged of the most composed beings, such as man. The latter would then have a size and a colour, but no particular size or colour.


Berkeley presents his famous critique of this doctrine of abstraction.

First, he declares that he does not possess this wonderful Faculty of Abstracting [...] Ideas 6.

On the other hand, he admits to having a quite different faculty: that of picturing ideas of particular things, and combining them. Thus, he can imagine a man with two heads, but he will have a particular colour and shape: The Idea of Man that I frame to my self, must be either of a White, or a Black, or a Tawny, a Straight, or a Crooked, a Tall, or a Low, or a Middle-sized Man. 7.

In fact, the general abstract idea is an impossibility in itself: I cannot by any effort of Thought conceive the abstract Idea above described. 8.

I can only separate qualities by thought if they can be separated in reality (e.g. imagine a man with one arm missing): I cannot conceive separately, those Qualities which it is impossible should Exist so separated 9.


Berkeley opposes Locke, who in An Essay Concerning Human Understanding, asserts that it is the faculty of forming abstract general ideas that makes man superior to the animal. He assumes that language implies the possession of general ideas. Yet this is a mistake for Berkeley:

A Word becomes general by being made the Sign, not of an abstract general Idea but, of several particular Ideas, any one of which it indifferently suggests to the Mind. 10.

In fact, Berkeley does not deny absolutely there are general Ideas, but only that there are any abstract general Ideas 11.

Here is what he thinks this type of idea corresponds to: An Idea, which considered in it self is particular, becomes general, by being made to represent or stand for all other particular Ideas of the same sort 12.

1 A Treatise Concerning the Principles of Human Knowledge, Introduction, §3
2 ibid., §7
3 ibid.
4 ibid.
5 §8
6 §10
7 ibid.
8 ibid.
9 ibid.
10 §11
11 §12
12 ibid.