Institutio Oratoria

The answer is that in such cases we must rely on feeling. It is possible to have an inadequate understanding of what it is precisely that makes for severity or charm, but yet to produce the required effect better by taking nature for our guide in place of art: none the less there will always be some principle of art underlying the promptings of nature.

It is, however, the special duty of the orator to realise when to employ the different kinds of rhythm. There are two points which call for consideration if he is to do this with success. The one is concerned with feet, the other with the general rhythm of the period which is produced by their combination. I will deal with the latter first. We speak of commata, cola and periods.

A comma, in my opinion, may be defined as the expression of a thought lacking rhythmical

A colon, on the other hand, is the expression of a thought which is rhythmically complete, but is meaningless if detached from the whole body of the sentence. For example O callidos homines [*]( From the lost pro Cornelio. O the cunning of those men! O what careful forethought! I ask you did one of us fail to note that such would be your action? ) is complete in itself, but is useless if removed from the rest of the sentence, as the hand, foot or head if separated from the body. He goes on, O rein excogitatam. At what point do the members begin to form a body? Only when the conclusion is added: quem, quaeso, nostrum fefellit, id vos ita esse facturos? a sentence which Cicero regards as unusually concise. Thus as a rule commata and cola are fragmentary and require a conclusion.