1. The right of private judgment involves two distinct issues which are often bundled into one:
i) The subjective source of private judgment
ii) The objective standard of private judgment.
Regarding (i), every professing believer, whether he’s a low churchman or high churchman, has to exercise his individual judgment. That’s inescapable. The high churchman is no exception to this necessity. It’s not as if the low churchman is an autonomous individual while the high churchman has no mind of his own. No, the high churchman thinks that his denomination, his tradition, is right. And that represents a personal value-judgment.
Regarding (ii), the rule of faith is external to us. Even though you apply it (the subjective dimension), what you apply is something over and above yourself (the objective dimension).
It’s like using a ruler. You use the ruler to measure an object. Indeed, you may use it to measure yourself.
But the ruler is a standardized measuring device, with standardized units, such as inches and feet. You didn’t create the standard.
2. At this point the high churchman says, “A perfect ruler is useless without a perfect measurer!”
Hence, it’s pointless for a carpenter to use a ruler unless he has an infallible apprentice to apply the ruler and take inerrant measurements.
Of course, in real life, carpenters manage to get along without infallible measurers.
For that matter, rulers and tape-measures are not mathematically precise to the nth degree.
3. But someone might object that I’ve oversimplified the relation between (i)-(ii).
Yes, the standard is external to us, but if there’s more than one claimant (to be the true standard), then by what criterion do we decide which standard is the true standard? Don’t we need a standard to identify the standard?
Whether this generates a genuine conundrum depends on how abstractly we put it. If a putative standard is internally inconsistent, then I can judge it on its own grounds. It will fall of its own dead weight.
For example, critics of sola scriptura typically attack it on the pragmatic grounds that sola Scriptura leads to certain consequences, which they deem to be unacceptable. So they regard the rule of faith as a problem-solving device.
But, in that event, what if the Catholic or Orthodox rule of faith generates its own set of problems? What if it fails to solve the problems it posed for itself?
Then that would falsify the Catholic or Orthodox rule of faith on its own grounds. It was supposed to be a solution, a practical alternative, to what was wrong with the Protestant rule of faith. But if it identifies a problem, puts itself forward as a solution, then fails to resolve the problem, we can discount it on its own terms.
And that wouldn’t falsify the Protestant rule of faith, since the Protestant didn’t buy into the assumption that a rule of faith must be a problem-solving device.
Of course, when I talk about internal consistency, or the lack thereof, that’s a logical standard. And it’s a standard which all parties share in common—except the fideist, who can never argue for fideism.
There’s also the issue of factual consistency. Is the rule of faith predicated on erroneous or dubious historical claims? For example, what’s the historical evidence for apostolic succession? How would you verify every link in the chain?
A Protestant believes in sola Scriptura, not because of some a priori, utilitarian condition it must meet, but on factual grounds. Is this the rule of faith that God imposes on his church? Is this what God requires of us? Is this the measure of our responsibility?
What has God revealed regarding the rule of faith—both in word and deed? What does he hold us to? How has he guided his people in the past? Do his prophecies or promises reveal a fundamental shift in divine policy?