Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
There is also another method of dividing bases into two classes: according to this disputes are either about substance or quality, while quality is treated either in its most general sense or in its special senses.
Substance is dealt with by conjecture: for in enquiring into anything, we ask whether it has been done, is being done, or is likely to be done, and sometimes also consider its intention: this method is preferable to that adopted by those who style the conjectural basis a basis of fact, as though we only enquired into the past and what has