"Or at least thoughts that can be related to experience. It became a matter of great importance to the British empiricists to scrutinize all human conceptions to see whether there was any basis for them in actual experience. But let us take one philosopher at a time."
"Okay, shoot!"
"The first was the Englishman John Locke, who lived from 1632 to 1704. His main work was the Essay Concerning Human Understanding, published in 1690. In it he tried to clarify two questions. First, where we get our ideas from, and secondly, whether we can rely on what our senses tell us."
"That was some project!"
"We'll take these questions one at a time. Locke's claim is that all our thoughts and ideas issue from that which we have taken in through the senses. Before we perceive anything, the mind is a 'tabula rasa'--or an empty slate."
"You can skip the Latin."
"Before we sense anything, then, the mind is as bare and empty as a blackboard before the teacher arrives in the classroom. Locke also compared the mind to an unfurnished room. But then we begin to sense things. We see the world around us, we smell, taste, feel, and hear. And nobody does this more intensely than infants. In this way what Locke called simple ideas of sense arise. But the mind does not just passively receive information from outside it. Some activity happens in the mind as well. The single sense ideas are worked on by thinking, reasoning, believing, and doubting, thus giving rise to what he calls reflection. So he distinguished between 'sensation' and 'reflection.' The mind is not merely a passive receiver. It classifies and processes all sensations as they come streaming in. And this is just where one must be on guard."
"On guard?"
"Locke emphasized that the only things we can perceive are simple sensations. When I eat an apple, for example, I do not sense the whole apple in one single sensation. In actual fact I receive a whole series of simple sensations--such as that something is green, smells fresh, and tastes juicy and sharp. Only after I have eaten an apple many times do I think: Now I am eating an 'apple.' As Locke would say, we have formed a complex idea of an 'apple.' When we were infants, tasting an apple for the first time, we had no such complex idea. But we saw something green, we tasted something fresh and juicy, yummy ... It was a bit sour too. Little by little we bundle many similar sensations together and form concepts like 'apple,"pear,"orange.' But in the final analysis, all the material for our knowledge of the world comes to us through sensations. Knowledge that cannot be traced back to a simple sensation is therefore false knowledge and must consequently be rejected."
"At any rate we can be sure that what we see, hear, smell, and taste are the way we sense it."
"Both yes and no. And that brings us to the second question Locke tried to answer. He had first answered the question of where we get our ideas from. Now he asked whether the world really is the way we perceive it. This is not so obvious, you see, Sophie. We mustn't jump to conclusions. That is the only thing a real philosopher must never do."
"I didn't say a word."
"Locke distinguished between what he called 'primary' and 'secondary' qualities. And in this he acknowledged his debt to the great philosophers before him-- including Descartes.
"By primary qualities he meant extension, weight, motion and number, and so on. When it is a question of qualities such as these, we can be certain that the senses reproduce them objectively. But we also sense other qualities in things. We say that something is sweet or sour, green or red, hot or cold. Locke calls these secondary qualities. Sensations like these--color, smell, taste, sound--do not reproduce the real qualities that are inherent in the things themselves. They reproduce only the effect of the outer reality on our senses."
"Everyone to his own taste, in other words."
"Exactly. Everyone can agree on the primary qualities like size and weight because they lie within the objects themselves. But the secondary qualities like color and taste can vary from person to person and from animal to animal, depending on the nature of the individual's sensations."
"When Joanna eats an orange, she gets a look on her face like when other people eat a lemon. She can't take more than one segment at a time. She says it tastes sour. I usually think the same orange is nice and sweet."
"And neither one of you is right or wrong. You are just describing how the orange affects your senses. It's the same with the sense of color. Maybe you don't like a certain shade of red. But if Joanna buys a dress in that color it might be wise to keep your opinion to yourself. You experience the color differently, but it is neither pretty nor ugly."
"But everyone can agree that an orange is round."
"Yes, if you have a round orange, you can't 'think' it is square. You can 'think' it is sweet or sour, but you can't 'think' it weighs eight kilos if it only weighs two hundred grams. You can certainly 'believe' it weighs several kilos, but then you'd be way off the mark. If several people have to guess how much something weighs, there will always be one of them who is more right than the others. The same applies to number. Either there are 986 peas in the can or there are not. The same with motion. Either the car is moving or it's stationary."
"I get it."
"So when it was a question of 'extended' reality, Locke agreed with Descartes that it does have certain qualities that man is able to understand with his reason."
"It shouldn't be so difficult to agree on that."
"Locke admitted what he called intuitive, or 'demonstrative,' knowledge in other areas too. For instance, he held that certain ethical principles applied to everyone. In other words, he believed in the idea of a natural right, and that was a rationalistic feature of his thought. An equally rationalistic feature was that Locke believed that it was inherent in human reason to be able to know that God exists."
"Maybe he was right."
"About what?"