Book 9
2.122
A comma, in my opinion, may be defined as the expression of a thought lacking rhythmical completeness; on the other hand, most writers regard it merely as a portion of the colon. As an example I may cite the following from Cicero: Domus tibi deerat? at habebas: pecunia superabat? at egebas. Or. lxvii. 223. See IX. ii. 15. But a comma may also consist of a single word, as in the following instance where diximnus is a comma: Diximus, testes dare volumus.
2.123
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.
