Our Knowledge of the External World

(Epistemology & Metaphysics)

VIII. From Rationalism to Empiricism

The Rationalists

Descartes (1596 – 1650)

Spinoza (1632 – 1677)

Leibniz (1646 – 1716)

The Empiricists

Locke (1632 –1704)

Berkeley (1685 – 1753)

Hume (1711 – 1776)

A. A vast change in philosophical outlook based largely on a change in Paradigms of Knowledge

1. For the Rationalists, the best example of knowledge was mathematics (particularly Euclidean geometry) which was certain, enduring and deductive.

2. The Empiricists had another model: Newton (1642 – 1727)

a. Newtonian physics was profoundly important knowledge that was discovered by looking at the world – using observation & experiment.

b. After Newton, knowledge based on experience became every bit as reputable as the sort of deductive knowledge found in Euclid.

“Nature, and Nature's laws lay hid in night:


God said, Let Newton be! and all was light.”

Alexander Pope (1688– 1744)

IX. John Locke: Common Sense Empiricist

A. A man of many talents & many careers

1. Political theorist, religious thinker, statesman, government official, physician AND the first great Empiricist philosopher.

B. Our Lockean Views

1. Political philosophy

a. Influence on Jefferson

2. Views that have become common sense in theory of knowledge

X. Locke’s Way Through The Screen of Perception

B. Locke’s Argument for the existence of an external world

1. Puzzles for solipsists

a. Our sensory experiences are largely beyond our control

b. Our sensory experiences exhibit a great deal of pattern and coherence

2. Locke’s explanation: Our sense data are caused by material substance which exists independently of our minds and obeys laws that are independent of our minds.

XI. Locke’s Account of Perception

A. Penetrating the screen of perception vs. describing the other side.

1. Having argued that matter exists, Locke must now tell us what it is like. How do we justify our beliefs about matter?

B. Naïve representationalism

1. All properties of our sensory experience accurately represent the properties of matter that cause them.

C. Locke’s limited representationalism

1. Some properties of our sensory experience resemble the properties that cause them; others do not.

a. Primary & Secondary Properties of objects in the external world: Primary Properties are those that do resemble the properties of the experiences that they cause. Secondary Properties are those that do not resemble the properties of the experiences that they cause.

i. Primary: motion, number, solidity, shape & size

ii. Secondary: color, taste, smell & temperature

b. Defending the distinction

i. The variance argument: The same external object can cause two incompatible sensory experiences.

(a). An experiment with 3 pails of water.

ii. The argument from Newtonian science.

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