Criticising Locke’s Primary and Secondary Quality Distinction
Berkeley’s Relativity Argument successfully shows that Locke’s primary/secondary quality distinction was flawed. It does not, however, deal Locke’s theory a fatal blow.
In An Essay on Human Understanding, Locke argued that any property which presents itself to people in two or more different ways cannot be intrinsic to that object; and therefore must be a secondary property. An example Locke used to support this was that:
If someone put their hands into a basin of water, and one of their hands was warmer than the other, then the water would feel cooler to one hand and warmer to the other.
From this, Locke argued, it follows that warmth-as-people-feel-it is not an intrinsic property of the water but a power of the water to affect people differently depending upon the circumstances. Other examples of secondary properties are that food tastes different to different people, or even to the same person at different points in their life; and the same also applies to smell.
Berkeley’s Relativity Argument
In his Principles of Human Knowledge and Three Dialogues, Berkeley argues against Locke’s primary/secondary quality distinction. One of Berkeley’s main criticisms said that the way Locke defined primary and secondary properties meant anything true of secondary properties was also true of primary properties.
To show this Berkeley posited that a building appears small from a distance and becomes larger and larger as someone approaches it. This showed that extension, according to Locke, is not an intrinsic property of an object but a power of that object (since it presents itself to people in different ways); making it a secondary property. The same, according to Berkeley, is true of all seemingly intrinsic properties of objects including shape, number and motion.
Discussing and Criticising Berkeley’s Relativity Argument
Berkeley’s point is a good one. People can only perceive the world from their own perspective and any property of an object that is perceived will potentially express itself to them and others in different ways (depending how far away they are standing from the object, the angle from which they see it, how fast they are moving, etc.). As a result extension, shape, motion and solidity of objects can all be argued to be nothing in the objects themselves.
Number Remains a Primary Property
The only property which is not a relational property in this way is number. Berkeley disagreed with this. He argued that because a measurement can be considered as one meter, one hundred centimetres, forty inches, etc. ‘number is entirely a creature of the mind.’ [Berkeley 1999, 29,] However Berkeley has made a mistake. After all, as Bennett points out in Locke, Berkeley, Hume: Central Themes, the item is objectively one meter, objectively one hundred centimetres and objectively forty inches, ‘and nobody’s mind has anything to do with it.’
The problem is that, “how long is that object?” might seem to make sense in everyday, colloquial language but it is logically too open ended. “As long as a piece of string,” or, “twice the distance of half its length,” are both valid answers to this question. Only by adding units into the phrasing of the question (for example “how long is that object in centimetres?”) do we gain logical completion of the sentence. This way there is no ambiguity about number when conceiving of objects.