Institutio Oratoria

if this is impossible, we should put aside whatever first occurs to us and reason with ourselves as follows:

What if this were not the case?

We must then repeat the process a second and a third time and so on, until nothing is left for consideration. Thus we shall examine even minor points, by our treatment of which we may perhaps make the judge all the better disposed to us when we come to the main issue.

The rule that we should descend from the common to the particular is much the same, since

what is common is usually general. For example,

He killed a tyrant

is common, while

A tyrant was killed by his son, by a woman or by his wife

are all particular.