Locke's Causal Theory of Perception

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  • 0:11 Mental vs. Physical Reality
  • 0:40 Representations of Reality
  • 1:49 Primary and Secondary…
  • 3:49 The Causal Theory of…
  • 5:01 Lesson Summary
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Lesson Transcript
Instructor: Christine Serva

Christine is an instructional designer, educator, and writer with a particular interest in the social sciences and American studies.

This lesson focuses on John Locke's explanations for how we understand the world and where these ideas originate. We'll look at how he viewed the role of sensations and what they cause us to experience.

Mental vs. Physical Reality

Is the world inside your own mind an accurate model for what the physical world really is? Does your perception come close to being a true, complete picture of the world, like a copy of it?

This lesson looks at these types of questions in relationship to the thoughts of philosopher John Locke and his causal theory of perception. He rejected the concept that your mind could produce ideas that match the precise truth about the physical world.

Representations of Reality

Locke argues we can never really form a complete picture of an object in our minds that matches the object itself as it really is in the material world. We can only have ideas about that object. For example, let's say you have a slice of lemon in your hand. You look at the lemon, you smell the lemon and then you take a taste of it.

Your mind will develop ideas about that lemon from your experience with it. You might even argue that your mental images about that lemon are pretty close to what it's really like in the physical world. Yet, Locke argues that your thought of what this lemon is can only be a representation of the reality of the lemon. It can never match the lemon exactly.

He says that our ideas about a physical object are perceptions based on sensations we've experienced, like when you observe and interact with the lemon. When we learn about an object with our senses by looking at it, touching it, smelling it, hearing it, or tasting it, we can gain information about what the object is like, even if it doesn't give us the ultimate truth about it.

Primary and Secondary Qualities

Locke distinguishes between two different types of qualities in an object: primary qualities and secondary qualities. He argues that the primary qualities are the undeniable properties of an object, like the size and shape of the lemon. These help us to create mental ideas for what an object is. Primary qualities are quite reliable for producing ideas that resemble the real thing, according to Locke.

On the other hand, secondary qualities of an object are attributes like the yellow color of the lemon and the sour taste that are subjective. Locke considers these secondary qualities to be the results of the action of primary qualities on the organs. What does Locke mean by this?

In the case of our lemon, our ideas involve more than just the primary qualities we can all pretty much agree on. We might agree that the lemon is three inches in length, but we won't necessarily agree on how sour it is. This is because perception also involves the secondary qualities that we experience when our own body interacts with the item.

Let's say that you have just had something very sweet. When you bite into that lemon, it will likely taste even more sour than it would if you had not just had something sweet. Another example is how it feels to jump in a pool of water when you've just had a cold shower versus when you have had a hot one. The water feels warm in one case but feels freezing in the other, even though the temperature of the pool has not changed.

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