Locke's concept of primary and secondary qualities, whilst intended to help us make sense of the limits of knowledge, also had an unintended use. Locke had argued that some of the information which we receive through our senses is subjective and should not be trusted (secondary qualities), whilst other information could be considered objective and constituted reliable knowledge (primary qualities).

From Locke's point of view, the thing that possessed these different qualities - the substance - could never really be known in itself. If, for example, we consider once again the example of the table, we can be aware of such things as its colour or texture (secondary qualities) or its shape and size (primary qualities). But we cannot know the thing itself because everything we experience about the table will come under one of these two categories.

Berkeley's Criticism of Locke

Berkeley considered Locke and other philosophers to have opened the door to atheism and scepticism by casting doubt on the senses. In an attempt to defend faith in God and knowledge from such attacks, Berkeley attempted to show that, rather than sensations of objects arising from powers in the object itself (as Locke thought), the experiences were in the perceiver (us).

What this means is that the object does not need to possess any powers with which it produces effects on our senses, because the object does not exist apart from our perception of it. This allows Berkeley to deny the sceptical argument that we do not see objects as they really are.

Berkeley's View of Reality

Arguments for Idealism

The main arguments for Idealism are based on the idea that our perceptions of objects are in us. In other words, when we say that an object is red, its redness is part of our perception of it, not in the object or - as Locke argues - an effect of some power of redness in the object.

So what arguments does Berkeley use? First he attacks the idea that secondary qualities can exist in the object:

1. Sensation. When you put your hand in cold water, the temperature feels different depending on the temperature of our hand. If your hand is hot, the water will feel colder; if your hand is cold, the water will feel warmer. The water cannot be hot and cold at the same time. Therefore the perception of temperature must be in the perceiver.
   
   
2. Taste. If a taste is pleasurable, such as the sweetness of sugar, how can we say that pleasure exists in the object itself (the sugar)? Therefore, since we cannot separate the taste of sweetness from our pleasure, both must exist in the perceiver and not in the object (the same obviously goes for displeasure).

Next he tries to show that some perceptions are relative, attacking both primary and secondary qualities:

3. Colour. If two people see the same object from different perspectives, one might think it was a different colour to the other. Both colours cannot exist in the object at the same time, so the colour must exist in the perceiver and not in the object.
   
   
4. Speed. If I am standing still and I see a train passing, the people on that train are moving at a certain speed, but to each other they appear to be sitting still. If speed exists in the object, how can the people on the train be both moving and at rest? The answer must be that the quality exists in the perceiver.

Here Berkeley trues to show that there is no difference between real and apparent qualities:

5. The Master Argument. Berkeley's main argument is meant to show that it is impossible for something to exist without being perceived (or, as he says, esse est percipi, Latin for "To be is to be perceived"). This means that if we cannot imagine what the perception of something must be like, we cannot really say that it exists. Berkeley uses this idea to attack the notion of substance or matter, for if all the qualities that we ascribe to it are either primary or secondary qualities, can we actually say that the substance itself exists?

Questions

Think about what problems there might be with this, especially:

1. What this view might mean for science.
2. How it might be possible to verify our perceptions.
3. Whether it is possible to prove or disprove Berkeley's argument.