Aristotle, Rhetoric
J. H. Freese, Ed.

[10] Hence, although the method of deliberative and forensic Rhetoric is the same, and although the pursuit of the former is nobler and more worthy of a statesman than that of the latter, which is limited to transactions between private citizens, they say nothing about the former, but without exception endeavor to bring forensic speaking under the rules of art. The reason of this is that in public speaking it is less worth while to talk of what is outside the subject, and that deliberative oratory lends itself to trickery less than forensic, because it is of more general interest.¹ For in the assembly the judges decide upon their own affairs, so that the only thing necessary is to prove the truth of the statement of one who recommends a measure, but in the law courts this is not sufficient; there it is useful to win over the hearers, for the decision concerns other interests than those of the judges, who, having only themselves to consider and listening merely for their own pleasure, surrender to the pleaders but do not give a real decision.²
That is why, as I have said before, in many places the law prohibits speaking outside the subject in the law courts, whereas in the assembly the judges themselves take adequate precautions against this.