The one, same, and only Sola Scriptura. I accept that folks (well, some folks) will use philosophy, history, tradition, their God-given minds, etc., to develop their Christian thoughts. However, if they submit these thoughts to examination by the light of Scripture as their "primary" authority, then they are engaging in "Scritpure Alone," or Sola Scriptura.
It doesn't matter where one gets their ideas from, or how many sub-authorities one deigns to submit to. When push comes to shove there is only one authority which is, ahem, authoritative. This authority stands alone, no other claim is given the least bit of creedence if it contradicts the one authority. This authority is solitary. There may be secondary and tertiary sources which are plural; but singular, one, is the final (or primary) authority.
There is thus only one authority. It is single. It stands alone, on its own plane, at the summit of judgeship. It is solitary, the only authority to which final judgment is rendered.
In other words it is Alone. Scripture is this authority. Hence it can safely be said that any Christian who holds Scripture as his "primary" authority holds it as his only authority. Ultimately. What other source of authority are you suggesting they hold as a "co-primary" authority?
SD