How can we know what exists?

If someone asked you “What exists?” you would probably point to the things around you and say “Everything!” If asked how you know if it’s real, you probably answer that you can see, hear, touch, smell, or taste it all. But some philosophers think that it’s not that simple. Our senses can be tricked and they might not tell the truth. Can we ever really know what’s real?

The perfect form

The ancient Greek philosopher Plato said that there are two types of reality. One is our world, with everything we see, hear, and touch. The second is another world full of perfect things that Plato called “forms.” He said that in our world we have only imperfect copies of forms that exist in another world. For instance, the dogs we see are less-than-perfect copies of the “form of dog.” Plato believed that we hold the idea of perfect forms in our minds, so we can
recognize the copies when we meet them.

A world of shadows

This imagined scene helps explain Plato’s idea of forms. Imagine a group of people who have been imprisoned in
a cave since they were born. They are tied up facing the back wall of the cave, which is all they can see. Near the cave
entrance there is a fire that casts shadows onto the back wall. Sometimes other people  walk along a path between the fire and the cave. They hold up puppets, which appear as shadows on the cave wall. Since this is all the prisoners have ever known, they think the shadows are real objects. Plato said that we are like these prisoners. We think the things we see and hear around us are real. In fact, they are like shadows of the real things, which are the forms.

Collecting information

Plenty of later philosophers disagreed with Plato’s ideas about reality. They didn’t believe we need perfect forms to explain how we know things, and they suggested instead that our minds gather information. Take an apple, for
example. Our senses tell us about its particular color, shape, feel, and taste. All this information is collected and organized in our minds. We see the fruit and immediately think “apple” because that’s the name we have been taught.

Just an idea?

When we see, hear, or touch something, we form an idea of what it is. So when we feel something fluffy and see brownness and big ears, we might decide this adds up to the idea of a “rabbit.” “Rabbit” is a human word and idea. But if “rabbit” is just an idea in your head, what do you really know? You know you have an idea, but do you really have a rabbit? And what happens if no one is around to have the idea—is there still a rabbit?

Only ideas are real

The suggestion that only ideas are real is known as “idealism.” It can seem very odd to ask yourself how you know something—say, a table— is there in front of you. Your senses give you information about it: it’s hard, wooden, has legs, and so on. But to figure out that this object is a table you have to use reason. Try altering some of the information. If the table moved, all by itself, would you change your mind about what it is? Magicians take advantage of our ideas about what is real to perform their tricks. They say, “See this? And this? But now watch— nothing is as you thought!”

Beyond our senses

Perhaps, as the idealist philosopher Immanuel Kant suggested, there are real things in the world outside our minds. Unfortunately, we have no way of knowing what they actually are. All we know about things comes from what we sense about them. But what if you had 10 different senses instead of just five? What would the world seem like to you then?

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