Laudator Temporis Acti

Cicero, On the Republic 1.25.38 (tr. Clinton Walker Keyes):

I will do as you wish, as well as I can, and shall at once begin my discussion, following the rule which, I think, ought always to be observed in the exposition of a subject if one wishes to avoid confusion; that is, that if the name of a subject is agreed upon, the meaning of this name should first be explained. Not until this meaning is agreed upon should the actual discussion be begun; for the qualities of the thing to be discussed can never be understood unless one understands first exactly what the thing itself is.

faciam, quod vultis, ut potero, et iam ingrediar in disputationem ea lege, qua credo omnibus in rebus disserendis utendum esse, si errorem velis tollere, ut eius rei, de qua quaeretur, si nomen quod sit conveniat, explicetur, quid declaretur eo nomine; quod si convenerit, tum demum decebit ingredi in sermonem; numquam enim, quale sit illud, de quo disputabitur, intellegi poterit, nisi, quid sit, fuerit intellectum prius.