 Where grammatical form tracks logical form, a non-paronymous noun will signify either a substance or a being in one of the nine Aristotelian categories of accidents, and a paronymous noun or a verb will signify that such a being is present in or attributed to some underlying subject. But metaphysics, as Fârâbî understands it, is not about things in the categories (Book of Letters I,11–17), but rather about the categories themselves (especially substance) and about trans-categorial concepts such as being, unity, essence, cause, and also God (who also, for Fârâbî, does not fall under any category). And where grammatical form tracks logical form, these concepts will be signified neither by non-paronymous nouns, nor by paronymous nouns or verbs, but by particles. Particles in an ideal logical language thus correspond roughly to what a modern philosopher would call logical constants. And it is clear that Fârâbî thinks that at least some important metaphysical notions were expressed in Greek by particles, or by terms morphologically derived from  particles.[18]  As noted above, the names of many of the Aristotelian categories in Arabic (and of some of them in Greek) either are particles or are morphologically derived from particles, and the scientific questions from Posterior Analytics II, which Fârâbî treats in Book of Letters Part III, are distinguished by their different interrogative words (“if/whether”, “what”, “why”), which in Arabic are all particles. And Fârâbî may well have thought that the Greek original of Metaphysics V was devoted to distinguishing the many meanings of particles (not just of words in general), not in the sense that the lexical items that head each chapter of Metaphysics V are in all cases themselves particles or even nouns morphologically derived from particles (although some of them  are),[19]  but in the sense that the many meanings of these nouns would track the many meanings of some particle, as the meanings of the noun “cause” (Metaphysics V,2) track the meanings of the particle “because”. There is in fact good reason to think this is true for a reasonable number of the chapters of Metaphysics  V.[20] Metaphysics V also discusses the categories of quantity and quality (V,13–14), where, as noted, the name of the category is derived from an interrogative word which is a particle in Arabic and which Fârâbî might well expect to be a particle in Greek (although in fact it is not), and the category of substance (V,8), where it is reasonable to say that the many meanings of “substance” track the many meanings of the question “what it is” from Posterior Analytics II and Book of Letters Part III, where again the interrogative word “what” (ti in Greek, mâ in Arabic) is a particle in Arabic. We can also reasonably say that the many meanings of “being” (V,7, on in Greek, mawjûd in Arabic) track the many meanings of the question “whether it is” from Posterior Analytics II and Book of Letters Part III (ei esti in Greek, hal mawjûd in Arabic), where the interrogative word “whether” is a particle in both languages. More surprisingly, although Fârâbî cites the Greek word for “being” as astîn = estin, which is in fact the third-person singular present-tense verb “is”, he says explicitly that this word is not a verb and that it is not a paronymous noun: his description of its functions implies that it also cannot be a non-paronymous noun, and so for Fârâbî this word must be a  particle.[21]