In the Liturgy video you mentioned that the Antiphons traditionally have three verses. I noticed that on great feast days or elevated commemorations there are more verses in the HTM book then just three. Is there a reason for this?
When we come across that, we have been continuing the antiphon with the verses. Is that they way to handle that situation?
Yes – Great Feasts tend to have four verses. There is a reason for this and it is a good example of liturgical archaeology.
The ancient order for antiphons is as follows:
Troparion (4x) with a verse before each
Both Now; Troparion
Troparion one final time with no verse.
If this looks familiar, it is because this is the order we follow during Bright Week and on the day of Pascha itself at the beginning of Vespers, Matins and Divine Liturgy.
As time went on, this practice evolved into two different practices:
Either, Troparion (3x) (Such as the end of Vespers and the beginning of Matins on Great Feasts)
Or, Troparion with 4 Antiphons (Such as in the Divine Liturgy).
When Antiphons became more popular and started replacing the Typika, three verses were picked instead of four. This practice has been (rightly, in my opinion) criticized by Fr. Konstantinos Papagiannis and he has proposed alternative antiphons that are all sets of four.