Sallust, in his history of Catiline’s conspiracy:
Per illa tempora quicumque rempublicam agitavere, honestis nominibus, alii, sicuti populi jura defenderent, pars, quo senati auctoritas maxuma foret, bonum publicum simulantes, pro sua quisque potentia certabant.
We proceed to a rule of a different kind. During the course of a period, the same scene ought to be continued without variation. The changing from person to person, from subject to subject, or from person to subject, within the bounds of a single period, distracts the mind, and affords no time for a solid impression. I illustrate this rule by giving examples of deviations from it.
_Honos_ alit artes, _omnesque_ incenduntur ad studia gloriâ; jacentque _ea_ semper quæ apud quosque improbantur.
Speaking of the distemper contracted by Alexander bathing in the river Cydnus and of the cure offered by Philip the physician:
Inter hæc à Parmenione fidissimo purpuratorum, literas _accipit_, quibus ei _denunciabat_, ne salutem suam Philippo committeret.
Hook, in his Roman history, speaking of Eumenes, who had been beat down to the ground with a stone, says,
After a short time _he_ came to himself; and the next day, _they_ put him on board his ship, _which_ conveyed him first to Corinth, and thence to the island of Ægina.
I give another example of a period which is unpleasant, even by a very slight deviation from the rule.
That sort of instruction which is acquired by inculcating an important moral truth, _&c._
This expression includes two persons, one acquiring, and one inculcating; and the scene is changed without necessity. To avoid this blemish, the thought may be expressed thus:
That sort of instruction which is afforded by inculcating, _&c._
The bad effect of this change of person is remarkable in the following passage.
The _Britains_, daily harassed by cruel inroads from the Picts, were forced to call in the Saxons for their defence, _who_ consequently reduced the greatest part of the island to their own power, drove the Britains into the most remote and mountainous parts, and _the rest of the country_, in customs, religion, and language, became wholly Saxons.
_Letter to the Lord High Treasurer. Swift._
The following example is a change from subject to persons.