According to Locke, what was the difference between primary and secondary qualities?
How did the paradox of the basins demonstrate this difference?
John Locke was an English philosopher and physician and he is commonly known as “father of liberalism”. Like Hobbes, he also opposed the existence of innate ideas and believed that sensory stimulations somehow caused the ideas in humans. For Locke, the ideas either come from sensory experiences or from the reflections of sensory stimulations. He was considered the first British empiricist and followed the traditions of Sir Francis Bacon.
According to Locke, the physical and secondary qualities referred to characteristics of the physical world and are very distinct. These two terms were borrowed from his friend Robert Boyle and it strongly influenced Locke’s philosophy. Locke defined the word quality as a physical object that have the power to produce an idea. He distinguished primary and secondary qualities in the following ways:
| Primary Qualities | Secondary Qualities |
| Primary qualities are those objects, which have power to produce ideas that correspond to the physical world. | Secondary qualities are those objects, which have power to produce ideas that do not correspond to the physical world. |
| He considered the primary qualities as physical reality and science. | According to him, secondary qualities are more subjective, not constant, purely psychological experiences and have no counterparts in the physical world. |
| Primary qualities include number, figure, motion, extensions, shape, and size and position. | Secondary qualities include taste, odor, color, sound and temperature. |
Arguments rose about the secondary qualities and the nature of ideas produced. Thus, Locke demonstrated the nature of idea caused by secondary qualities through paradox of basins. He considered one of the secondary qualities, that is, temperature to demonstrate the nature of idea. He used three basins for the demonstration – basin A filled with cold water, basin B filled with hot water and basin C filled with warm water.
When a person places the hand, one in basin A and other in B, he can feel one as cold and other as hot. This shows temperature in a physical quality. But when the person placed both the hands in basin C, the hand previously placed in basin A will feel hot and the hand previously placed in basin B will feel cold. Though there was warm water in basin C, the hands felt different temperatures due to the previous experience and hence, he proved that temperature is the secondary quality.