Modern materialists seem to take it as self-evident that 'secondary qualities' are completely subjective and don't exist outside of the mind (except in whatever esoteric way they are communicated to the senses through a medium, like vibrations in air molecules hitting the ear drum for sound, wavelengths of light interacting with the rods and cones in the eye for color, and so on). Both would basically be the yard stick by which all other 'things' are measured, and so could easily be analogous, it seems like. But I can just hear Philonous saying, 'What! Have you any evidence of this three-dimensional space beyond the immediate qualities you perceive?' To which I'd be forced to answer, 'Well, no.'Īlso, it just seems like a point that Berkeley would be more than happy to grant, because what I call 'the universe at large' seems awfully alike to the impartial and perfect perceiver (God). So basically, it has an absolute extension in relation to 'the universe at large'. My own thinking is something along the lines of: If space is conceived of as a three-dimensional area, then an object has an absolute extension within that three-dimensional area, regardless of any observer. But I'd like to know if there are any serious rebuttals to the above argument or if the attitude is more 'idealism is absurd there's no reason to argue against it'. While in grad school, it seemed to me that metaphysics was mostly regarded as a 'dead category' (or at least an incredibly uninteresting one, except as it related to the history of philosophy), one without any intriguing questions, and that the field was now essentially relegated to the abstract physicists to figure things out. In thinking about this, it really does seem like the materialist is backed into a metaphysical corner. You may at any time make the experiment by looking with one eye bare and with the other through a microscope. Does it not therefore follow from this, likewise, that it is not really inherent in the object? But as we approach to or recede from an object, the visible extension varies, being at one distance ten or a hundred times greater than at another. Again, have you not acknowledged that no real inherent property of any object can be changed without some change in the thing itself?

Why then I shall be obliged to think they too exist only in the mind. But what if the same arguments which are brought against secondary qualities will hold proof against these also?

You are still then of the opinion that extension and figures are inherent in external unthinking substances. I am rereading Berkeley's Three Dialogues between Hylas and Philonous and am curious about any subsequent works which actively rebut his dismissal of primary qualities.

Berkeley dialogues