One must presume that long and short arguments contribute to the same end. (Epicurus, Gnomologium Vaticanum, 26)
In a rigorous normative manner, Epicurus starts his advice with the verb ‘must’ (dei). But what does determine a norm for logos or argument?
A norm for the length of arguments that are expressed in natural language, not in a logical one, could be imposed by the participants to a certain conversation, as Socrates repeatedly requests to his interlocutors in Plato’s dialogues.
When the call for brevity of arguments is asked by some participants to a conversation, the norm shows to be a means of controlling the speakers and only afterwards the arguments they use.
Because the length of arguments is caused by the desires of their authors to extend their individuality in the field of conversation. Persuasiveness overwhelms and ignores the truth, as Plato endeavors to say in Socrates’ name.
But the will for persuasiveness is also supported by the nature of arguments. They do not oppose to any will of making them long or short. And they do not turn the speaker to their end: a discourse seems to last even if the speaker ceases to utter it. It remains in others’ mind.
The property of arguments of being indifferent to length and time could be responsible for speaker’s choose of long discourses. He has the chance to reach the values of extension and eternity, otherwise difficult to meet in other facts of life. Moreover, he has the chance to state his own extension and his own time, so that the audience is easily made to believe that what is heard represents the world itself. The persuasiveness always implies that those who are persuaded do not search for a confirmation in the world.
Plato holds that the subject matters of the arguments can provide the brevity of arguments, while Epicurus invokes their end: the same end for long and short arguments. Both of them measure the discourses by appealing to something placed outside them.
Referring to their end, Epicurus posits a value that is in direct contradiction to the seemingly endless nature of the arguments. The end appears at the natural limits of arguments and has the force to oppose to their speaker, too, since he also has an end. Therefore, the end shows to be a norm for brevity that comes from the arguments themselves and restricts the speaker in his entirety.
Of course, the speaker may fight for long discourses even more boldly, if he wants to defy the end. However, if he wants to ground his personality as a definite whole, he would learn from Epicurus that the end provides also the property of being the same. The end as the logical law of reduction provides precision to the logical arguments, too.
A charitable interpretation of Plato’s dialogues would say that the Forms as subject matters of the short arguments are rather limitative means of controlling the length of discourses, than starting points for speculative images. In this case, the end and something that ends the arguments and the self-pride of their speaker are the same.