Why the idefinite article here

Question

The Horn of Winter, he thought, still confused from sleep. But Mance never found Joramun’s horn, so that couldn’t be. A second blast followed, as long and deep as the first.

AlpheccaStars · Accepted Answer

VoytaszekA second blast followed, as long and deep as the first.

We don't know how many blasts there will be. "A second blast" = one of a possible series; there is more to come.

The first = A specific, particular blast that occurred in the past; the first of a series. The most recent one or ones, where more is expected to come, use the indefinite article.

e.g.

The first blast sounded at precisely 6:00 pm. The second came fifteen seconds later, followed by a third. 
The first blast  sounded at precisely 6:00 pm. The second came fifteen seconds later, followed by a third, a fourth and a fifth in rapid succession.

Why the idefinite article here

Top answer

Get the Weekly English Kit 📬