During the era of the Enlightenment there was a debate among physicists as to the nature of reality. There were two metaphysical conceptions of qualities of matter. John Locke was the proponent of the distinction between primary and secondary qualities of matter. According to him, primary qualities are those that are objective facts pertaining to an object, which remain universally true irrespective of the perception of the observer. For example, a rectangular plate will remain a rectangle and under no conditions can one describe it as a circular object. Locke went on to assert that secondary qualities are those given rise through the senses of the observer. These include the color, smells, sound and taste of the object. These qualities are subjective to the particular observer and there could be divergence in how they are sensed. For example, an apple might taste sweet for one person while another might think it tastes bland. Locke contended that this dichotomy of qualities existed for all real objects in our world. (Jolley, 1999)
George Berkeley wrote a sharp polemic on Locke’s treatise. For Berkeley, only those inputs that are sensory can be considered ‘real’ in any sense of the term. The idea of an object existing outside the conception of a human mind, as an objective reality, is theoretically possible, but practically irrelevant. Berkeley argued that the only way that physical objects could be treated in philosophical discourse is by referring to their secondary qualities. To talk of an object in exclusion, as some entity within the co-ordinates of space and time, is impossible.
Jolley, N. (1999). Locke: His Philosophical Thought. Oxford, England: Oxford University Press.
Stirling, J. (2002). Introducing Neuropsychology. New York: Psychology Press.
Withers, C. W. (2007). Placing the Enlightenment: Thinking Geographically about the Age of Reason. Chicago: University of Chicago Press.