Perception and theExternal World

1

Direct Realism is 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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1. What we see is bent.

2. The pencil is not bent.

3. So what we see is not the pencil.

3

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

4

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?

5

Representative realism is the doctrine that sensations are caused by external objects and that our sensations represent those objects.

6

Locke believes that 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?

7

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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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.

9

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

Berkeley claims that material objects cannot exist because it’s impossible to conceive of something that exists unconceived. (Once you conceive of it, it’s no longer unconceived!)

10

Since one cannot conceive of something existing unconceived, Berkeley concludes that it’s impossible for something to exist unconceived.

Thus, everything that exists must be conceived by someone.

11

If to be is to be perceived, it would seem that when we stop perceiving something it ceases to exist.

But although we may stop perceiving something, God never stops perceiving anything.

So God holds things in existence by thinking about them.

12

There once was a young man who said “GodMust think it exceedingly oddIf he finds that this treeContinues to beWhen there’s no one about in the quad”

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Dear Sir: Your astonishment’s oddI am always about in the quadAnd that’s why the treeWill continue to beSince observe by Yours faithfully,God

14

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.

15

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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