Locke on Knowledge
(Essay, Book IV)

Early Modern Philosophy

I. What Kinds of Things Do We Know About?

4.1.1: All our knowledge is simply knowledge of our own ideas, because our ideas are the only immediate objects of our knowledge. This is a consequence of Locke’s representative theory of perception, a view sometimes known as the veil-of-perception view.

Since our only immediate acquaintance is with our ideas, Locke says that all our knowledge must be knowledge of the agreement or disagreement of ideas. This agreement or disagreement is of four different kinds (4.1.3):

Identity or diversity. This is simply a matter of recognizing two ideas as the same or not the same: the idea of white is the same idea as the idea of white but a different idea from the idea of red. [It’s perhaps not as straightforward as Locke makes out, though, given Locke’s lumping together of the notion of a perception with the notion of an idea, and his lumping together of the intrinsic properties of an idea with properties of the thing the idea represents. Suppose I look at a piece of chalk and get from it the idea of white. Then I look at a piece of paper and get from that an idea of white (a very slightly different shade, perhaps). Are those two ideas the same idea, or not the same idea, for Locke? They are both ideas of white, but they are ideas of different shades of white.]

Relation. (E.g. the idea of a dozen is the idea of a larger quantity than the idea of one. Locke himself would probably say that the idea of a dozen is larger than the idea of one, but that confuses properties of the idea with properties of what it represents: a foot is larger than an inch, but there’s no reason the idea of a food should have to be “larger” than the idea of an inch, if indeed ideas can be said to have sizes at all.)

Coexistence, or Necessary Connection. By this Locke means two properties of a substance both of which flow from its essential nature and which hence are guaranteed always to go together in that substance. (Suppose all the people I’ve seen (a) have noses, (b) have hearts, and (c) are under seven feet tall. (a) and (b) flow from their natures, and will always be found in people, while being less than seven feet tall need not be. So (a) and (b) coexist in people, while (c) does not coexist with (a) and (b).)

Real existence. By this Locke means the existence of something corresponding to an idea that we have. But isn’t it odd to call this a matter of the agreement or disagreement of ideas? Isn’t it rather a matter of the agreement or disagreement of ideas with the world?

II. The Degrees of Knowledge

Locke, like Descartes and Spinoza, distinguishes between three degrees or levels of knowledge. These are:

Intuitive knowledge. This is the most secure kind of knowledge; it corresponds to Descartes’ notion of things we perceive by the natural light, and which are so obviously true that we can’t doubt them.

Demonstrative knowledge. This is the kind of knowledge we have of most mathematical truths: we can’t just see that they are correct, but we can prove them on the basis of axioms of which we have intuitive knowledge, by means of very small and simple steps which we can intuitively perceive must be valid.

Sensitive knowledge: the knowledge of the existence of things that we acquire by sensing them. (Here Locke needs to respond to Cartesian worries; he does so jokingly in 4.2.14, and more seriously in 4.11.)

III. The Extent of Knowledge

identity and diversity: we have intuitive knowledge of the identity or diversity of all our ideas.

relation: it’s hard to say. We can know a lot about mathematics and morality this way; not clear how much else. Most of this knowledge is demonstrative, and is a matter of “finding intermediate ideas.”

coexistence: we don’t know much about this (because it’s hard to distinguish constant conjunction from necessary connection).

real existence: we have intuitive knowledge of our own existence (just as Descartes thought); we have demonstrative knowledge of God’s existence; of the existence of other things we have only sensitive knowledge, and that only works while we’re actually sensing the thing in question.

Last update: March 16, 2009. 
Curtis Brown  |  Classical Modern Philosophy   |  Philosophy Department  |   Trinity University