Among the happy circumstances which in the fifth century B.C. favoured the development of Hellenic art must be reckoned as an important element the peculiar distinctions and relations of the Hellenic dialects. These relations were such as it would probably be difficult to parallel. The several idioms, most of them separately cultivated up to the standard of literature, differed from each other sufficiently to make their broad characters readily perceptible, and yet resembled each other sufficiently to be mutually intelligible. Each of the great branches of the cousinhood had its own characteristic product, and the total of these was the common inheritance of the nation. The language thus resembled an organ with several sets of stops; poetry was at once provincial and classic; and the literature enjoyed by a felicitous balance the conflicting advantages of fixed and fluctuating speech. That the great artists of Athens perceived their own strength is in a general way sufficiently obvious. The distinction between the Doric chorus and the Attic dialogue is alone a proof of the fact. But it seems not unlikely that closer examination may reveal to us more subtle applications of the same method, and that, besides the keener perception which we may thus gain of the tone and feeling of particular passages, we may even be able to employ our knowledge of such laws as an instrument of criticism and interpretation. This paper is an attempt to represent under this aspect the facts respecting the use by the three tragedians of the substantives and adjectives in -οσυνος and -οσυνη.