The peripatetic philosophy, obeying rationalist propensities, has tried to eternalize the common-sense categories by treating them very technically and articulately. A 'thing' for instance is a being, or ENS. An ENS is a subject in which qualities 'inhere.' A subject is a substance. Substances are of kinds, and kinds are definite in number, and discrete. These distinctions are fundamental and eternal. As terms of DISCOURSE they are indeed magnificently useful, but what they mean, apart from their use in steering our discourse to profitable issues, does not appear. If you ask a scholastic philosopher what a substance may be in itself, apart from its being the support of attributes, he simply says that your intellect knows perfectly what the word means. But what the intellect knows clearly is only the word itself and its steering function. So it comes about that intellects SIBI PERMISSI, intellects only curious and idle, have forsaken the common-sense level for what in general terms may be called the 'critical' level of thought. Not merely SUCH intellects either--your Humes and Berkeleys and Hegels; but practical observers of facts, your Galileos, Daltons, Faradays, have found it impossible to treat the NAIFS sense-termini of common sense as ultimately real. As common sense interpolates her constant 'things' between our intermittent sensations, so science EXTRApolates her world of 'primary' qualities, her atoms, her ether, her magnetic fields, and the like, beyond the common-sense world. The 'things' are now invisible impalpable things; and the old visible common-sense things are supposed to result from the mixture of these invisibles. Or else the whole NAIF conception of thing gets superseded, and a thing's name is interpreted as denoting only the law or REGEL DER VERBINDUNG by which certain of our sensations habitually succeed or coexist. Science and critical philosophy thus burst the bounds of common sense. With science NAIF realism ceases: 'Secondary' qualities become unreal; primary ones alone remain. With critical philosophy, havoc is made of everything. The common-sense categories one and all cease to represent anything in the way of BEING; they are but sublime tricks of human thought, our ways of escaping bewilderment in the midst of sensation's irremediable flow.