Hello! Welcome back to our exploration of epistemology.
In our last lesson, we explored the "value problem," questioning why knowledge is more valuable than a simple true belief that gets us the same practical result. Plato's answer was that knowledge is more stable, "tied down" by justification, making it resilient.
This raises a crucial question we've yet to address: where do our beliefs—the very building blocks of knowledge—come from in the first place? Over the next few lessons, we'll explore the primary sources of belief, starting with our most immediate connection to the world: perception.
Today's lesson addresses the first of these sources. Our goal is to explain perception as a source of knowledge, a view known as empiricism, and to understand its potential fallibility. This will take us into one of the most significant historical debates in philosophy.
Empiricism: Knowledge Through the Senses
The philosophical view that knowledge is primarily derived from sensory experience is called empiricism. Empiricists argue that our minds begin as a "blank slate," and all the ideas and knowledge we accumulate throughout our lives come to us through our senses.
The most famous proponent of this view was the 17th-century English philosopher John Locke. Let's start with a short video that introduces his core idea.
Locke, Berkeley, & Empiricism: Crash Course Philosophy #6
This clip from CrashCourse Philosophy introduces John Locke and his foundational empiricist concept of the 'tabula rasa,' or blank slate.
Please watch the segment from 02:43 to 03:16. It quickly explains Locke's belief that we are born without innate ideas and that all knowledge comes from experience.
Locke believed that this "experience" comes in two forms:
- Sensation: Information from the external world via our five senses (sight, sound, touch, taste, smell).
- Reflection: Information from the internal world of our own minds (thinking, doubting, believing).
To solidify this foundational concept, the following reading expands on Locke's view.
lecture: introduction to John Locke
This text, from an online lecture on John Locke, provides a clear, concise explanation of how all ideas originate from experience.
Read the section titled 'II. All ideas come from experience.' It's a short section that defines sensation and reflection as the two modes of experience.
The Problem: Is Perception Reliable?
Empiricism places a massive amount of trust in our senses. But how trustworthy are they? On the surface, our perception seems to give us a direct and accurate picture of reality. This common-sense view is sometimes called Direct Realism: the idea that we perceive mind-independent objects and their properties directly.
However, a little critical thinking—something you're keenly interested in—reveals that our senses can be easily fooled. Given your background in graphic design, you are likely familiar with how visual information can be manipulated to create experiences that don't match reality.
Philosophers use these kinds of examples—along with others like illusions, hallucinations, and perceptual variation—to challenge the simple idea that we directly perceive the world as it truly is.
The following video explores these challenges to Direct Realism in detail. As you watch, focus on the problems being raised, as they are classic illustrations of why perception can be a fallible source of knowledge.
Knowledge from Perception: Direct Realism, Indirect Realism, and Idealism (Epistemology Episode 2)
This video from the channel philosophymania explains the common-sense theory of Direct Realism and then systematically outlines the problems it faces, such as perceptual variation and illusions.
Watch the segment from 01:36 to 11:30. Pay close attention to the arguments from 'perceptual variation' (like Bertrand Russell's table example) and 'illusions' (the bent chopstick). These directly address the fallibility of perception.
A Classic Solution: Primary and Secondary Qualities
The fallibility of perception poses a serious problem for empiricism. If our senses can't be trusted, how can they be the foundation of knowledge?
John Locke was well aware of this problem. His solution was to make a distinction between two types of qualities that we perceive.
- Primary Qualities: These are qualities that exist in the objects themselves, independent of who is perceiving them. They include solidity, size, shape, motion, and number. We can all agree on these through measurement.
- Secondary Qualities: These qualities are not in the objects themselves, but are powers in the objects to produce certain sensations in our minds. They include color, sound, taste, and smell. These are subjective and can vary from person to person (or species to species).
Let's watch a quick explanation of this distinction.
Locke, Berkeley, & Empiricism: Crash Course Philosophy #6
Returning to the CrashCourse video, this segment uses the example of an apple to clearly explain Locke's distinction between primary and secondary qualities.
Watch from 03:16 to 05:28. Notice how the apple's measurable properties (primary) are separated from its subjective properties like color and taste (secondary).
This is a clever move. Locke isn't saying our senses are completely wrong. He's saying that what we perceive is a combination of objective reality (primary qualities) and our mind's interpretation of it (secondary qualities).
For a deeper dive into this fascinating idea, let's turn back to the text on Locke. It uses a very helpful modern analogy.
lecture: introduction to John Locke
This reading offers a more detailed explanation of primary and secondary qualities, using the famous 'tree falling in the forest' thought experiment and a powerful analogy to an electronic 'transducer'.
Please read the section titled 'IV. Ideas are caused in us by qualities'. Focus on how the text explains that what exists in the world (e.g., impact waves) is different from what exists in our minds (e.g., the sensation of sound). The transducer analogy is particularly insightful.
Locke's theory is an early form of Indirect Realism (or Representative Realism). It suggests that we don't perceive the world directly; instead, we perceive our own mental representations (ideas) which are caused by, and represent, the external world. This acknowledges the fallibility of perception while trying to save it as a source of knowledge about the world.
Test your understanding!
Imagine you and a friend are looking at a painting. You say the blue of the sky is "vibrant," while your friend, who is color-blind, says it looks "dull gray." Using Locke's framework, how would you explain this disagreement? Which aspects of the painting would you both agree on?
Show answer
According to Locke, the disagreement about the color of the sky is a disagreement about a secondary quality. The color "blue" is not in the painting itself; rather, the paint on the canvas has a certain texture and chemical composition (primary qualities) that gives it the power to produce the sensation of "blue" in most human minds. Your friend's different visual apparatus causes that same power to produce a different sensation ("dull gray"). Neither of you is "wrong" about your subjective experience.
However, you would both agree on the painting's primary qualities. You could both measure its dimensions (size), agree on its rectangular shape, its weight (solidity), and that it is one painting (number). These qualities are in the object itself, not just in your minds.
Conclusion
Today we took our first step in exploring the sources of our beliefs, focusing on perception. We've seen how empiricism champions sensory experience as the foundation of knowledge, but also how that foundation can be shaky.
Key Takeaways:
- Empiricism is the philosophical view that all knowledge originates from experience, primarily through our senses.
- The common-sense view that we perceive reality directly (Direct Realism) is challenged by the fallibility of perception, as demonstrated by illusions, hallucinations, and perceptual variation.
- John Locke proposed a solution by distinguishing between primary qualities (objective properties like size and shape) and secondary qualities (subjective properties like color and sound, which are powers in an object to cause sensations in us).
- This distinction leads to a view known as Indirect Realism, where we perceive mental representations of the world, not the world itself.
Preview of the Next Lesson:
The unreliability of our senses led many philosophers to question whether perception could truly be the ultimate foundation of knowledge. If our senses can be so misleading, where can we find certainty? In our next lesson, we will explore the main alternative: rationalism, the view that reason, not experience, is the primary source of knowledge.