The kinds of rhetoric art are three in number; for this much is the number of the listeners of rhetorical speeches too. A rhetorical speech consists of three parts: of the speaker, of what one says, and of the person to whom it is addressed, while the end of the speech refers to him, I mean the listener. The listener, therefore, must be either a spectator or a judge, and a judge either of what is done or of what is about to be. And it is the member of the assembly that judges what is about to be, the juror what is done, and the spectator the skill of the rhetorician. Hence, there must be three kinds of rhetorical speech: deliberative, forensic, and epideictic speech.
The deliberative speech either exhorts or deters, since those who counsel either aside or publicly in the assembly do one of these two. The forensic speech either accuses or defends; for litigants necessarily do one of these two. The last one the epideictic speech either praises or blames.
Again, time appropriate to each of these: to the deliberative the future (for he who counsels, whether he exhorts or deters, does so about things to come, to the forensic the past (for it is always about things done that one accuses and the other defends himself), while to the epideictic the present; for all those who praise or blame do so with regard to the existing condition of things, though many times they do make use of the past, when they wish to recall things past, but also of the future, when they wish to foretell.
Now the end of each speech is different, and being three speeches there are three ends as well: of the deliberative kind the expedient or harmful; for he who exhorts does so in view of a better course, all other considerations, i.e. if it is just or unjust, noble or disgraceful, are included into the speech for the sake of that. Of the forensic kind the just or unjust; here too the others are included for the sake of them. Again those who praise or blame have in view what is noble or disgraceful, and they too attach the others for the sake of the former. A sign of this, i.e. that the above mentioned ends are the real ones, is the fact that there are cases in which one would not dispute about the other points, e.g. a man in custody might admit that he is the one who did it or has done harm, but he would never confess that he is unjust — for there would not even be need of a trial. Similarly, those who counsel quite often lay the other considerations aside, however they would never admit that they are recommending what is inexpedient or deterring from what is useful — that it is unjust to enslave the neighbors and those who do not injure, they oftentimes do not give a fig.
Similarly, those who praise or blame do not consider whether there acts have been expedient or harmful, but they often thing it is praiseworthy that one has ignored his own interest to do what was noble, e.g. they praise Achilles because he was of help to his comrade Patroclus knowing that he must die, though he might have lived. To him such a death is nobler, while living more expedient.
Bibliography: Aristotle, Art of Rhetoric (1358a.36 to 1359a.5)
Translation: George Kotsalis