Metaphysical notions such as being, unity, essence, and cause are signified by particles rather than by nouns or verbs in an ideal logical language.

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