What better or clearer method, for the commencement of instruction of this nature, can there be than discussion of the term advanced, so distinctly, that all who use the same language may follow it? Is the term for demonstration of such a kind as the word Blityri, which is a mere sound, signifying nothing? But how is it that neither does the philosopher, nor the orator,—no more does the judge,—adduce demonstration as a term that means nothing; nor is any of the contending parties ignorant of the fact, that the meaning does not exist?
Philosophers, in fact, present demonstration as having a substantial existence, one in one way, another in another. Therefore, if one would treat aright of each question, he cannot carry back the discourse to another more generally admitted fundamental principle than what is admitted to be signified by the term by all of the same nation and language.
Then, starting from this point, it is necessary to inquire if the proposition has this signification or not. And next, if it is demonstrated to have, it is necessary to investigate its nature accurately, of what kind it is, and whether it ever passes over the class assigned. And if it suffices not to say, absolutely, only that which one thinks (for p. 559 one’s opponent may equally allege, on the other side, what he likes); then what is stated must be confirmed. If the decision of it be carried back to what is likewise matter of dispute, and the decision of that likewise to another disputed point, it will go on ad infinitum, and will be incapable of demonstration. But if the belief of a point that is not admitted be carried back to one admitted by all, that is to be made the commencement of instruction. Every term, therefore, advanced for discussion is to be converted into an expression that is admitted by those that are parties in the discussion, to form the starting point for instruction, to lead the way to the discovery of the points under investigation. For example, let it be the term “sun” that is in question. Now the Stoics say that it is “an intellectual fire kindled from the waters of the sea.” Is not the definition, consequently, obscurer than the term, requiring another demonstration to prove if it be true? It is therefore better to say, in the common and distinct form of speech, “that the brightest of the heavenly bodies is named the sun.” For this expression is more credible and clearer, and is likewise admitted by all.