What is sola scriptura about?

Catholic apologists routinely raise uncomprehending objections to sola scriptura. In fairness, this isn't entirely their fault. During the Reformation and Counter-Reformation, both sides were making things up on the fly, so there's room for improvement. We can refine our positions and tighten our formulations.

1. Sola scriptura is a two-stage principle: the fundamental principle concerns the primacy of divine revelation. Nothing is higher than or equal to the authority of divine revelation/communication.

In the context of sola scriptura, divine revelation means public revelation. Revelation for the church. Obligatory for God's people. As distinguished from private topical revelation.

That by itself isn't sola scriptura. There are phases in redemptive history where revelation was oral as well as written.

2. Sola scriptura is an extension of the primary principle (the primacy of public revelation): the era of public revelation is past. The record of public revelation is only found in Scripture. Indeed, Scripture was written for posterity. Certain things committed to posterity because we no longer have public revelation and memory is too unreliable and subject to manipulation.

3. Notice that sola scripture is an abstract principle. Sola scriptura is a claim about the status of the Bible but not a claim about the content of the Bible or how we know the content of the Bible. It could be expressed in conditional terms: If the Gospel of John is Scripture, then it outranks uninspired sources.

4. We might compare sola scriptura to the rules of poker. The rules of poker are about the nature of poker, but they're not about a particular game of poker. They don't describe or predict any particular game of poker. The rules of poker are norms that dictate what's permissible or impermissible in poker, but they don't tell you how many cards are still in the deck halfway through the game or which players hold which cards, or which players have a winning hand or losing hand or if a player has a gun up his sleeve.

5. To illustrate the point, imagine a parallel universe in which all the books of the canon are different. But that wouldn't invalidate the principle of sola scriptura since the principle operates at a more abstract level: the primacy of revelation. In a parallel universe, the revelatory books might all be different from the Protestant canon, but the principle remains the same. It's just that the parallel universe has an alternate religious history.