Michael Lacewing

Rationalism on sensory experience

THE DIFFICULTY OF DEFINITIONS The terms rationalism and empiricism have been used in different ways at different times, and sometimes quite misleadingly. They have been applied to theories of knowledge, theories of concept acquisition, theories of justification, and historical schools of thought. The main question that divides them is what are the sources of knowledge? How do we acquire it?. We can ask the question about our concepts as well how do we get those? Rationalism gives an important role to reason, and empiricism to experience. But we may well wonder why we have to choose; in acquiring knowledge, dont we use both reason and experience? However, there is a clear way of marking the difference between rationalism and empiricism, which has become common in philosophy. The distinctions we drew above help us: Rationalism claims that we can have synthetic a priori knowledge of how the world is outside the mind. Empiricism denies this. Terminology All three parts of the definition are important. Substantive knowledge: this word marks the distinction between analytic and synthetic truths. A proposition is substantive if it is synthetic, i.e. if it is not true or false just in virtue of the meanings of the words. Knowledge that isnt substantive is trivial, analytic. Many trivial truths are obvious: all bachelors are unmarried; but some are not: your uncles fathers nieces sole female cousin is your mother (think about it!). A priori knowledge: a priori knowledge is knowledge that does not require (sense) experience to be known to be true. Propositions that can only be established through experience are a posteriori. This distinction is about how to check or establish knowledge. It is not (in the first instance) a claim about how we acquire the concepts or words of the proposition. Babies are not born knowing that all bachelors are unmarried! Yet this is a truth that clearly doesnt need testing against experience; we know it is true just by knowing what it means. How things stand outside the mind: it is not obvious how we know what we know about our own mental states. Propositions about my mental states are not analytic, but substantive: that I feel sad or am thinking about unicorns. They dont require sense experience to be known; in fact, does knowing my own thoughts involve experiencing them at all? We dont need to worry about this. Rationalists and empiricists alike do not deny that we just do know that we have certain impressions and ideas, thoughts and feelings. The argument is about knowledge of things other than our own minds. So: rationalists argue that it is possible for us to know (some) substantive facts about how the world outside our own minds is without relying on sense experience. Empiricists argue that it is not. Notice that they dont deny that all a priori knowledge

no empiricist claims that you have to check whether all bachelors are unmarried to see if it is true! They simply claim that all a priori knowledge is trivial. And likewise, rationalists dont deny that sense experience can give us knowledge; they only argue that there is some knowledge we can have that doesnt rely on sense experience.

PLATO: KNOWLEDGE, THE FORMS AND THE PHYSICAL WORLD The exception is Plato. He argues that particular things, which all objects of experience are, cannot be objects of knowledge, because they will always both be X have some property, e.g. beauty or largeness and not-X, either at different times, or to different observers, or in different contexts. And so

can we say that any one of these many things is, any more than it is not, what anyone says it is? (Republic, Bk. V, 479b)

By contrast, the Form of X is X under all conditions, to all observers, at all times. Plato argues that we cannot know what is not the case, and if something both is and is not X, then we cannot know that it is X. From this Plato argues that if we consider just the many things that are X, we shall form beliefs about them, but cannot acquire knowledge; whereas if we consider the unchanging Form of X, we acquire knowledge and understanding. His argument turns (and many would say, falls) on the assumption that each level of understanding has corresponding level of reality in its object, i.e. what it is about. What does not exist is related to ignorance; absolute unchanging reality is known; belief relates to what is between what is (X) and what is not (X), i.e. the changing particulars of the world around us. Belief and knowledge are not the same thing, as belief can be false whereas knowledge cannot. Therefore that about which we have beliefs cannot be the same thing as that about which we have knowledge. Belief relates to the world of the senses, knowledge to the world of the Forms. In the Republic, it appears that Plato asserts that belief and knowledge are not the same thing, that the progression from belief to knowledge is transformative. There is considerable debate as to what the proper understanding of his theory is at this point. But whatever the right interpretation, we are certainly forced to consider whether knowledge could be a type of belief, e.g. justified true belief, or whether it is something essentially different. On this matter, perhaps Platos Theaetetus, in which he develops the justified true belief theory, is more influential. Plato sets the standard for knowledge very high. Because knowledge by definition cannot be false, it seems he believes that we must be certain of our knowledge in order to have knowledge. If we cannot be certain, we cannot know. In the case of the Forms, the certainty derives (in large part) from the unchanging nature of the object of knowledge. However, some philosophers have argued that once we have achieved knowledge of the Forms suggests we can then have knowledge of the world of the senses too. E.g. we will understand how a particular is X and not X, and so wont form false beliefs about it.

DESCARTES: KNOWING THROUGH REASON The wax argument The notion of change and difference in objects of the senses also leads Descartes to argue that knowledge, even of physical objects, relies on reason in an important way. Following Bernard Williams (Descartes, Ch. 8), the famous wax argument goes roughly like this: when I melt a piece of wax, it loses all of its original sensory qualities (taste, smell,

tactile qualities, shape); yet I believe it is the same wax. So the wax is not its sensory qualities. So when I think of the wax, I am thinking of something that is extended and

changeable. I think that the possible changes it can go through outstrip what I can imagination. So its not through my imagination that I have my conception of the wax. Rather,

and somewhat surprisingly, I perceive (comprehend) the wax through my understanding.

The wax I think of this way and the wax I detect through my senses is the same wax. Although we say we see the wax (through vision), in fact we judge (through

understanding) that it is present from what we see. The correct interpretation of the argument has been much discussed. However, if we notice its context in this Meditation and in the Meditations as a whole, we should be inclined to think that the argument is more about our knowledge of material objects than the nature or existence of material objects. So Descartes is not attempting to assert the identity conditions of the piece of wax, he is noticing that our conception of the wax doesnt appear to depend on its particular sensory qualities. So what is our conception? That the wax is something that endures through such changes (it is changeable), but also that it is extended (takes up space). If this is our conception of the wax, then it is not a conception derived from our senses, but an intellectual conception of it, and as such, given by our understanding. Descartes question is not what is the wax?, but what is our idea of the wax?. At first, our idea of the wax is of something defined by its sensory properties. But this is muddled. When we realize that we comprehend the wax through understanding, as something extended and changeable, our comprehension of the wax has become clear and distinct. We also realize that talk of seeing the wax is misleading. We judge or infer the presence of material objects from our sensory experiences. The material world This doesnt yet show that material objects really are extended we may have got an entirely wrong-headed conception of them. But in Meditation V, Descartes says that we have not, because we have a clear and distinct conception of them as extended, and what is clearly and distinctly conceived is true. So material objects really are extended, if they exist at all. Meditation VI argues that they do exist, and that we can know this. We have experiences which appear, very forcefully, to be experiences of a world external to our minds. These experiences must have some cause which is sufficient to cause them (see Meditation III). The options are: a real external world or God. In fact, there is a third option Descartes doesnt consider his own mind. But the experiences are involuntary, and if they were caused by his own mind, they would be voluntary. Because he knows his own mind, he would know if they were voluntary; but they arent, so God and the external world really are the only two options. If the cause was God, this would mean

that God was a deceiver because He would have created us with a very strong tendency to believe something false. But we know that God is not a deceiver. So there must really be an external world. Having established this, Descartes is quite happy our senses inform our understanding about particular physical objects, which then judges whether they exist or not. It is worth noting that, from Meditations II and V, we can know that the external, material world is an extended world. Sensory qualities do not properly belong to material objects; only extension is of their essence.