as philosophy


Russell’s Defence: External World as the best Hypothesis

Justify an external world as the best explanation going

A complete proof is beyond us, but it’s reasonable to believe in an external world as this explains why we have the sense data that we do.

An apple that I hide in a drawer can be found again when I return to it because it exists independently to me.

External world - Apple continued to exist when I had forgotten about it and it decayed

It is simpler to suppose objects exist independently of us than that my experience is an extended dream using the example of his cat.

“If the cat exists whether I see it or not, we can understand that it will become hungry”

“If we suppose it ceases to exist, just why the cat should become hungry in the interim becomes mysterious”


Idealism is the view that what is real depends upon the mind; does a material world exist outside of the mind? We know we have a mind, we know we perceive various colours and shapes, as so on. But to suppose that there is a material world that causes these sensations is a leap that we do not need to make.

Berkeley’s Idealism

Berkeley called sense data, or whatever we are immediately aware of, Ideas and claimed that physical objects do not exist independently of minds, but in reality are collections of such ideas. Immediate objects of perception are mind-dependent and there is no external world beyond our perception. 

All the contents of our minds must come from experience. 

If we have a concept but cannot find anything in experience from which it could have come, then we do not really have the concept at all.

A blind person, for an empiricist, cannot have the concept of the colour red, since they have not had any experience of red. 

Concept of matter or physical stuff

According to indirect realists, matter is something that we cannot experience as it lies behind the veil of perception. It is the cause of our experience but not something that we can experience directly. 

Berkeley argues; if we accept that we cannot experience matter, then it follows that we cannot have a concept of it. The concept ‘material objects’ is empty of content. For this reason Berkeley claimed the indirect realist’s talk about ‘matter’ was meaningless and that a concept of an unperceived thing was a contradiction. 

“To be is to be perceived”

Berkeley is denying that physical objects have an existence independent of perception. An object, on Berkeley’s account, is no more or no less than a cluster of ideas or sense impressions.

Berkeley’s attack on the primary/secondary quality distinction

Berkeley says that he cannot conceive of an object which has no qualities other than the primary. 

If an object can only be conceived with both primary and secondary qualities then our ideas of secondary qualities are inseparable from the primary. If we accept that our perceptions of secondary


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