Why did Berkeley reject John Locke’s distinction between primary and secondary qualities?

George Berkeley rejected John Locke’s distinction between primary and secondary qualities because he argued that both types of qualities are fundamentally the same: they are both "sensible ideas" that exist only within the mind.12

Locke had proposed that primary qualities (such as size, shape, and motion) resemble properties inherent in physical objects, while secondary qualities (such as color, taste, and smell) are merely powers of an object to produce sensations in the perceiver. Berkeley challenged this by asserting that there is no meaningful way to separate these qualities. He argued that primary qualities, like extension and impenetrability, are just as dependent on perception as secondary qualities. For instance, he noted that "extension" must be understood as either visual or tactile extension—both of which are ideas presented to the mind through the senses.321

Ultimately, Berkeley concluded that because all knowledge is derived from perception, we have no basis to claim that primary qualities exist in an imperceptible "material substrate" outside the mind. Since all sensible objects are composed of ideas, he maintained that both primary and secondary qualities exist only in the mind.12