You may have observed that in dividing up a verse into feet, the divisions must often be made within the words themselves, so that the boundaries between feet rarely correspond to the boundaries between words. When the end of a foot also coincides with the end of a word, the resulting division is called a diaeresis (> Gk. "division").

A diaeresis differs from a caesura in two respects. First, it occurs between, not within, feet. Second, it does not necessarily mark any discernible pause in the sense. Figure H shows these differences at work.

Again, the caesura clearly marks the sense-pause between cano and Troiae, while the diaeresis—even though it marks a division between the fourth and fifth feet, as well as between qui and primus—shows no pause in the sense. So, why bother to mark a diaeresis at all?

The answer is that a division like the one shown in Figure H is perceived as a distinct metrical unit with a life of its own. In other words, primus ab oris ends the verse with a very recognizable "dum-diddy dum-dum" (or "shave and a haircut"), a rhythmic snippet made all the more recognizable by the fact that primus begins a new foot.

The diaeresis between feet four and five, such as the one above, is called the bucolic, after the Greek boukolos, "herdsman," because the dactylic poetry of herdsmen was famous for "shave and a haircut" line endings.