Christopher Goodman

March 14, 1997

I wish to defend and support John Locke's "The Causal Theory of Perception" because it is a logical argument with many useful applications. Primarily, this argument allows us to make more objective judgments about the world we perceive - it allows us to more accurately see reality by telling us how to separate the object itself from our own opinions or qualitative value judgments about the object. However, just the fact that a particular theory is useful does not mean that the theory itself is correct, even though that might be the motive for trying to prove its correctness. Therefore, I must also address George Berkeley's argument, put forth by his character Philonous in Three Dialogues Between Hylas and Philonous, that "to exist is to be perceived."

To tackle Berkeley's argument, I will take Hylas and Philonous's Tree Argument. This is a nice variation on the common riddle of "If a tree falls in the middle of a forest, and no one is there to hear it, does it make a sound?" Philonous is trying to prove that everything that exists is perceived, and therefore exists only in the mind. If this is true, then nothing exists without the mind, and it is therefore pointless to distinguish between primary and secondary qualities as Locke does. Philonous challenges Hylas to conceive of any sensible object that exists without the mind. Hylas responds with the idea of a tree existing by itself, independent of, and unperceived by, any mind whatsoever. Philonous then points out that this is a contradiction - conceiving a thing that is unconceived. However, these two riddlers are failing to take into consideration one crucial element - time.

Now, I intend to prove that things can and do exist even though we do not perceive them. My argument rests on this presumption: It is possible for us to conceive things that do not exist and to conceive not to exist things that do exist, and that time allows us to see what really exists and what really does not exist, at the very least for some things. If we truly believe an object (for example, a chair) to exist, we will be able to see it, to touch it, to hear it's sound. We will be able to do all of the above until we have a reason to believe that it does not exist. Notice that I have included several different senses in this example, including the sense of touch. However well we might perceive this particular chair to exist, if it is not real, we will fall to the floor if we try to sit in it. That is because our action of sitting depends on the chair being solid and actually existing.

Now, let us imagine me walking from the patio of a friend's home into the den. I turn and face the house and walk towards the doorway, heading towards the nice comfortable sofa. Suddenly, I am knocked flat on my back. Looking up, I see the sun reflecting off a perfectly cleaned sliding glass door. Up until the moment I hit the glass, I had no idea that it was there, or no conception of the door. However after being knocked down, and also seeing the reflection, I now know that the glass exists. There is Hylas's needed example of an object that is both conceived and unconceived. I had no conception of the object before I hit it, but does that mean that the object did not exist until I hit it? No, for what necessarily follows is that the object suddenly came into existence just as I ran into it. That is absurd, for can there be any possible explanation for the spontaneous existence of a glass sliding door? Time allows the avoidance of contradiction in the idea of conceiving a thing which is unconceived - we may later confirm the existence of an object of which we had not even conceived earlier.

So, we now have the necessary establishment of the existence of objects independent of the mind. This is necessary for Locke's Causal Theory of Perception since it rests on the distinction between ideas, our perceptions that exist in our minds about objects, and qualities, powers in separate existing objects to produce ideas. We may have ideas independent of objects altogether, ideas about an object that do not arise from the specific object we are perceiving, ideas about an object that arise from the quantitative aspects (those aspects that are actually existing) of the object, and ideas that are caused by the quantitative aspects, but that are really just relative judgments about an object.

It is those final two ideas that concern Locke and form his idea of making a distinction between Primary Qualities and Secondary Qualities. Among the primary qualities are solidity, extension, figure, motion, number, temperature, etc. One way to look at these qualities is that they can be measured - they can be described in mathematical terms. Among the secondary qualities are colors, sounds, hotness/coldness, etc. These are subjective - they are all relative.

The secondary qualities are subject to our interpretation. They are judgments that we make about some thing, that are dependent upon the primary qualities. To illustrate this, Locke uses his water example. If one's hands are at different temperatures with each other, one "cold" and the other "hot, and the hands are then put into a tub of water that is of relatively moderate temperature, then to one hand the water feels warm and to the other it feels cool. But is not the water the same temperature throughout? Almost definitely yes, but the hands do not perceive it to be so. Therefore, our hands are making a qualitative judgment about the temperature of the water - a relative decision as to whether the water is hot or cold. Now, this is different from the actual temperature of the water - that is qualitative (it can be measured), but as far as our feeling of touch goes, determining temperature is much more a relative thing than a qualitative thing. Therefore, hotness/coldness is a secondary quality.

Extension, though, is a primary quality. We might make qualitative judgments about an object based on this primary quality - we may say that an object is large. This, though, is a relative term. However, we can measure the volume of an object and thus know in quantitative terms about the objects extension.

Locke gives another good illustration with his flame example. A flame can have a definite temperature - a primary quality of something that exists. It can also have warmth - a secondary quality that we see in the object that is closely related to the primary quality, but is a value judgment. And there can be the perception of pain - an idea which exists only in the mind, independent of the flame, even though associated with it.

If one accepts these ideas, one has a useful tool to help oneself be objective about a certain thing. If we remember these distinctions, then we can identify and separate from each other those qualities which exist in the object itself, those judgments we make about those qualities, and those ideas we have independent of an object. Separating primary qualities from secondary qualities allows us to more accurately perceive reality.