2.6 Locke’s Causal Theory of Perception

Jan 12, 2020 | ch2 Perception & Sensation, Cognitive Psychology, Courses

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.

Secondary qualities produce effects in the body that are not objective, that not everyone would agree on. These qualities are what make our picture of reality less than a precise match to what it really is. The sourness of the lemon and the temperature of the pool are just a couple of examples.

The Casual Theory of Perception

It may help to remember Locke’s theory by thinking of how when you look through the keyhole of a lock, you can see part of the picture but not all of it. You see a representative of what’s on the other side of the door, but it’s not an exact copy of what’s beyond the door.

In this case, one side of the door is physical reality and on the other side are you and me, each with our own mental reality. These mental realities involve ideas about what that world is like, but they are nowhere near a photocopy of that reality.

Why are Locke’s ideas on this topic referred to as the causal theory of perception? In his view, objects have qualities that cause us to have sensations, like when we perceive the qualities of a lemon and then develop ideas for what the lemon is like.

In other words, Locke believes there is a real, physical world, and our sensations help us create a mental understanding of that world. Although it’s not perfect, this representation of reality we develop through our senses and experience is the best information we have available to us.

Lesson Summary

According to the causal theory of perception, objects have qualities that cause us to have sensations. Objects have both primary and secondary qualities. Primary qualities are the undeniable properties of an object, like the size and shape, while secondary qualities are the results of the action of primary qualities on the organs, like the sour taste of a lemon.

Locke believes in the existence of a physical reality that is separate from our mental realities. He argues we can never really form an accurate copy 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 based on our experiences.

Learning Outcomes

After completing this lesson, you should be able to:

  • Explain Locke’s casual theory of perception and his idea that our representations of reality can never match actual reality
  • Describe and differentiate between the primary and secondary qualities of objects
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