Hence, all that was needed to arrive at the negation of matter or absolute spiritualism was to efface the distinction which he had drawn between primary and secondary qualities, and to call all sensible qualities, without exception, secondary. Locke recognizes, with Descartes and Hobbes, that color is nothing apart from the sensation of the person seeing it, that sound exists only for the hearing, that taste and smell are mere sensations, and do not inhere in the things themselves. And that is where he is wrong. Just as color, smell, and taste exist only for the person perceiving them, so extension, form, and motion exist only in a mind that perceives them. Take away the perceiving subject, and you take away the sensible world.
Existence consists in perceiving or being perceived.
That which is not perceived and does not perceive does not exist. The objects do not exist apart from the subjects perceiving them. Hence, there is no real difference between things and our ideas of them. The words sensible thing and idea are synonymous. Our ideas, or the things which we perceive, are visibly inactive.