I'm reading W. T. Jones account of Berkeley's theory, and I find that in general Berkeley convincingly demonstrated some weak points that are fundamental to Locke's theory. But there is one of his particular argument which I don't get the point:
In Jones' book "A History of Western Philosophy Vol 3: Hobbes to Hume", the author first cite a passage for Berkeley original work "A Treatise Concerning the Principles of Human Knowledge":
They who assert that figure, motion, and the rest of the primary or original qualities do exist without the mind, in unthinking substances, do at the same time acknowledge that colours, sounds, heat, cold, and suchlike secondary qualities, do not; which they tell us are sensations, existing in the mind alone, that depend on and are occasioned by the different size, texture, and motion of the minute particles of matter. . . . Now, if it be certain that those original qualities are inseparably united with the other sensible qualities, and not, even in thought, capable of being abstracted from them, it plainly follows that they exist only in the mind. But I desire any one to reflect, and try whether he can, by any abstraction of thought, conceive the extension and motion of a body without all other sensible qualities. For my own part, I see evidently that it is not in my power to frame an idea of a body extended and moving, but I must withal give it some colour or other sensible quality, which is acknowledged to exist only in the mind. In short, extension, figure. and motion, abstracted from all other qualities, are inconceivable. Where therefore the other sensible qualities are, there must these be also, to wit, in the mind and nowhere else.
Then the author gives his own comment:
This argument is extremely effective against Locke and Descartes, who held that color, sound, and odor are mind-dependent and yet denied that size and shape are. Strictly speaking, however, the argument shows only that primary and secondary qualities are "inseparably united." Hence those who did not agree with Locke and Descartes that the known facts about physiology "conclusively demonstrated" the mind-dependence of sense qualities would not be touched by this argument as it stands.
My problem is that I fail to see how this particular argument of Berkeley comes to be effective. I my understanding, by mind-depence of secondary qualities Locke doesn't mean these are fabricated by minds, but only that the objects have primary qualities and their primary qualities simultaneously cause us to perceive primary and secondary qualities. How does pointing out that primary and secondary qualities as perceived by us are "inseparably united" gonna undermine this position of Locke? It seems to me quite irrelevant…