Of some nouns on the other hand the denotation is more limited; and by the aid of the limitation we have before our minds not the common nature, but a limitation of anything, having, so far as the peculiarity extends, nothing in common with what is of the same kind; as for instance, Paul or Timothy.  For, in a word, of this kind there is no extension to what is common in the nature; there is a separation of certain circumscribed conceptions from the general idea, and expression of them by means of their names.  Suppose then that two or more are set together, as, for instance, Paul, Silvanus, and Timothy, and that an enquiry is made into the essence or substance of humanity; no one will give one definition of essence or substance in the case of Paul, a second in that of Silvanus, and a third in that of Timothy; but the same words which have been employed in setting forth the essence or substance of Paul will apply to the others also.  Those who are described by the same definition of essence or substance are of the same essence or substance ὁμοουσιοι. when the enquirer has learned what is common, and turns his attention to the differentiating properties whereby one is distinguished from another, the definition by which each is known will no longer tally in all particulars with the definition of another, even though in some points it be found to agree.