DP 9-10

Section 7.2 Facing Reality

Perception and the External World

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Direct Realism

• The doctrine that perception puts us in direct contact with reality.

• “Direct” because nothing comes between the world and our perception of it.

• “Realism” because there is an external world that is not affected by our thoughts.

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The Argument from Illusion

1. What we see is bent.

2. The pencil is not bent.

3. So what we see is not the pencil.

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Sense Data

• Sense data are the objects that are immediately known in sensation, such as colors, sounds, smells, hardnesses, roughnesses, etc.

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The Problem of the External World • We can’t compare our sense data with

the world; all we can do is get more sense data.

• So how can we know what the world is like in itself?

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Representative Realism

• The doctrine that sensations are caused by external objects and that our sensations represent those objects.

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Thought Probe: Hypothesizing the External World

• Locke: the hypothesis of an external world provides the best explanation of our sense data.

• Compare that hypothesis with the dream hypothesis. Which does better with regard to the criteria of adequacy: simplicity, scope, conservatism, and fruitfulness?

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Primary vs. Secondary Qualities • A primary quality is one possessed by material

objects such as: solidity, extension, figure, and mobility.

• A secondary quality is one that exists in the mind but not in material objects themselves such as: heat, color, taste, etc.

• According to Locke, sense data of primary qualities resemble the qualities of material objects.

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Berkeley on Primary and Secondary Qualities • Primary qualities such as figure and

extension are as variable as secondary qualities.

• What looks round from one angle can look elliptical from another.

• Consequently, they can’t be considered to resemble qualities of physical objects.

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Thought Experiment: The Inconceivability of the Unconceived

• Material objects are supposed to exist even when no one is thinking about (conceiving of) them.

• But it’s impossible to conceive of something that exists unconceived. (Once you conceive of it, it’s no longer unconceived!)

• Thus the notion of a material object is self-contradictory.

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Esse et Percipi: To Be is to Be Perceived • Since one cannot

conceive of something existing unconceived, it’s impossible for something to exist unconceived.

• Thus, everything that exists must be conceived by someone.

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God and Reality

• If to be is to be perceived, then when we stop perceiving something it ceases to exist.

• But God never stops perceiving anything.

• So God holds things in existence by thinking about them.

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Knox’s Limerick – Young Man’s Query There once was a young man who said “God

Must think it exceedingly odd If he finds that this tree Continues to be When there’s no one about in the quad.”

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Knox’s Limerick – God’s reply

Dear Sir: Your astonishment’s odd I am always about in the quad And that’s why the tree Will continue to be Since observe by Yours faithfully, God

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Phenomenalism

• Berkeley held that things are nothing but patterns of sensations.

• According to phenomenalism, all talk of things is reducible to talk of sensations.

• Objection: What we perceive depends on the state of our bodies, but the state of our bodies cannot be reduced to sensations.

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Conceiving the Unconceived

• It is not possible to conceive of something that exists unconceived.

• But it is possible to conceive that something exists unconceived.

• Thus the notion of material objects is not self-contradictory.

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