=182.= The analysis of the first two categories, those of Substance and Quality, leads us at once to the profoundest problems of Metaphysics; and even if we allow that the difficulty is primarily grammatical, and resolves itself into a discussion of the functions of Substantive and Adjective, it is none the less inextricably interwoven with all our habits of thought. It would be unreasonable to expect from the Stoics perfectly clear and consistent language on this point; they absorb into their system much from popular philosophy, and much from the teaching of Aristotle in particular. The view which is distinctively Stoic is that Substance and Quality are both body[51], but in two different aspects. The terms ‘body’ and ‘substance’ refer to the same reality, but do not describe it with the same fulness. Yet because the very word ‘substance’ (οὐσία) suggests existence, the Stoics are drawn also to speak of ‘substance without quality’ (ἄποιος οὐσία), and seem to identify it with a dead ‘matter’ (ὕλη), or ‘substratum’ (ὑποκείμενον), as though life must be introduced into it from without[52]. This is practically the view of Aristotle, embodied in the phrase ‘matter without quality is potentially body’[53]; but just so far as terms of this kind imply a dualistic explanation of the universe, they are not really reconcileable with the fundamental principles of Stoicism, and they must therefore be understood with reservations. It may often seem that the three terms ‘body,’ ‘substance,’ ‘matter,’ are practically interchangeable, but they are of different rank. For body exists eternally of itself; whereas substance and matter, except when loosely used as equivalents of body, do not exist of themselves, but substance always in association with quality[54], and matter always in association with force. Further we may distinguish between ‘substance’ in general, or ‘first matter,’ which is a ‘substratum’ (ὑποκείμενον) to the universe, and the ‘matter’ of particular things[55]. The former never grows greater or less, the latter may alter in either direction[56]. [Sidenote: Quality.]