Polysyndeton is the deliberate use of more conjunctions than grammar requires — and this, and this, and this — where ordinary usage would drop all but the last.
The effect is to slow a list down. Each conjunction forces a small pause, so the items arrive one at a time instead of as a set, and the passage acquires a sense of accumulation or exhaustion.
From the Sermon on the Mount in the King James Bible: “And the rain descended, and the floods came, and the winds blew, and beat upon that house.” Strip the conjunctions and you have a weather report. Keep them and the disasters pile up, each one landing separately.
Its opposite is asyndeton, which removes conjunctions entirely to produce speed rather than weight.
Polysyndeton works by making a list feel longer than it is. Four items joined by three ands occupy more attention than the same four separated by commas, because each conjunction is a beat the reader has to pass through. The technique is therefore useful wherever quantity is the point — endurance, abundance, relentlessness.
It is also why the device can quietly overstate. A sequence of modest items given polysyndetic treatment acquires a weight the items do not individually deserve, and a reader absorbed in the rhythm may register many where the actual count is four.
The device belongs to the oldest layer of English prose style, which is why it reads as biblical or archaic even when the subject is not. That association is a resource and a risk: used sparingly it lends gravity, and used often it sounds like someone impersonating gravity.
