Locke's way: Justification can be less than certain
The obvious thing to do is to weaken the justification condition, to require not indefeasible evidence but just good evidence.
As Moore pointed out, we normally take it that we know that we have hands, even though we do not have indefeasible evidence that we have them. The evidence that we have hands—which is the evidence of our senses—is strong evidence, even if it isn't strong enough to satisfy Descartes.Let us examine the proposal, then, that to know something
a) you must believe it,
b)it must be true, and
c) you must have good—but not necessarily indefeasible— evidence for the belief.
On this theory, unlike Descartes', I can know, for example, that I have two hands, because I have very good evidence from experience for my true belief that I have two hands. Someone who believes that evidence of this sort is what we require for knowledge of the physical world is called an empiricist. Empiricism is the claim that most or all of our beliefs are justified by experience—by empirical evidence, as it is called. Such evidence comes from our senses: our sight, hearing, taste, smell, touch, and so on. Just as rationalists regard necessary truths—sentences that must be true—as the model of knowledge, empiricists regard contingent truths—which might not have been true—as the model. (We shall discuss the idea of truths being necessary or contingent in the next chapter.) For a rationalist like Descartes, “2 + 2 = 4” would be a very good example of something we know, because reasoning can give us indefeasible evidence that it is true.
For an empiricist, a sentence such as “It is raining here,” said by someone standing in the rain, would be a very good example of something someone knows.Descartes was a leading rationalist. The English philosopher John Locke, who also wrote in the seventeenth century, was one of the founders of modern empiricism. In Book Two, Chapter One, Section 2, of his Essay Concerning Human Understanding, one of the great classics of empiricism, he says:
All Ideas come from Sensation or Reflection. Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas: how comes it to be furnished? Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, experience. In that all our knowledge is founded; and from that it ultimately derives itself.
Though this is an apparently clear statement of the essentials of empiricism, what Locke is saying is not as simple as it seems. There are two main reasons.
First, Locke held a special view about what our minds contain. Our knowledge, he believed, is stored in our minds in the form of collections of ideas. These ideas are what he calls the “materials” of knowledge: they are quite literally what our knowledge is made of. When he says that all our knowledge is founded in experience, then, he does not mean that all of our knowledge is justified by experience. He means rather that we can have no ideas that are not derived from experience; and that, therefore, every piece of knowledge is made up of materials that come from experience. As we shall see in a moment, it is very important that Locke did not hold that all of our knowledge has to be justified by experience.
A second reason why what Locke says here is not as simple as it seems is that Locke meant by “experience” something rather more than just sensation.
In Book Two, Chapter One, Sections 3 and 4, he argues that there are two sources of ideas in experience:The Objects of Sensation one Source of Ideas. First, our Senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them This great source of most of the ideas we have, depending
wholly upon our senses, and derived by them to the understanding, I call SENSATION.
The Operations of our Minds, the other Source of them. Secondly, the other fountain from which experience furnisheth the understanding with ideas is,— the perception of the operations of our own mind, as it is employed about the ideas it has got;... I call this REFLECTION, the ideas it affords being such only as the mind gets by reflecting on its own operations within itself..............................................................................................................................
These two, I say, viz. external material things, as the objects of SENSATION, and the operations of our own minds within, as the objects of REFLECTION, are to me the only originals from whence all our ideas take their beginnings.
All of our ideas, then, come from experience: either experience, in sensation, of the world outside us, or experience, in reflection, of the workings of our own minds. It is also true that most of our beliefs derive from experience. But, Locke holds, we can also come to know things—mathematical truths, for example, such as “2 + 2 = 4”—by reasoning, which he calls “demonstration.” “Mathematical demonstration,” he says, “depends not upon sense” (Book Three, Chapter Eleven, Section 6). Even here, however, our knowledge is founded in experience: for our ideas of the numbers 2 and 4, or of addition and the equality of numbers, are just as much derived from experience, according to Locke, as our ideas of tables and chairs.
The idea of the number 2, for example, he thought was derived by “abstraction” from our experiences of pairs of things.It follows, then, that though Locke stresses that our ideas come from or are “founded in” experience, he can agree that reason can be as much a source of knowledge as experience. Locke can, therefore, accept all the kinds of knowledge that Descartes' theory allowed: but he is not restricted to truths known indefeasibly. So he can hold that we sometimes come to know things other than by reasoning.
Empiricism as an approach to epistemology has grown side by side with modern science. Locke was a contemporary of Sir Isaac Newton, the first great modern physicist. This connection between the growth of empiricism and the growth of science is not very surprising. Science depends a great deal on experience in its search for knowledge of the physical world. Even psychology, which sometimes relies on our experiences of our own mental life for its evidence, relies on experience, in Locke's sense. For, remember, Locke regarded “reflection,” by which he meant our experience of our own mental lives, as a kind of experience.
The basic idea that much of our knowledge derives from our experiences of the world is, as a result, an attractive one in an age of science. Mathematics is, of course, important to modern science too, and we learn mathematical facts not from experience but—as Locke pointed out—by using our powers of reasoning. But even in mathematical physics, which uses more mathematics than most other sciences, the evidence of experience is tremendously important.
Nevertheless, it is one thing to say that we know only those things that we correctly believe and that experience—or demonstration— justifies us in believing; it is another to say precisely how our experiences justify our beliefs. Indeed, we have already come across the fact that creates the main problem for empiricism: the evidence of experience is always defeasible. This means that the evidence we have could, in each case, be misleading us. So we have to ask whether there is any way of deciding which evidence we should actually rely on. In answering this question, empiricists have often tried to develop the idea that some of the knowledge we acquire in experience provides the basis for the rest of our knowledge. They have held, in effect, that all of our knowledge is founded on one basic class of things we know. This approach is called foundation- alist epistemology.
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