Plot Railroading: How much?

[BRC]

My point is that, ultimately, the "forcing" comes from the fact that the GM *has* determined what encounters must happen and in what order.

That design is a prerequisite for the "forcing". If you don't have that, there's no need.

Also, by my definition, the outcome is equally certain. If the GM has already prepared the full list of encounters, then the outcome is, for all practical purposes, predetermined. The fact that the forcing doesn't need to happen if the situation happens to go that way is nice, but the structure is still the same, and the GM would absolutely do the "forcing" if necessary.

By pointing out the underlying structure, we can also look at the advantages of such a structure - the disadvantages are obvious. But by having a known, smaller space to work with, it's much easier for a GM to do a more detailed, thoughtful job of prep of the specific encounters. So long as players are okay with this, they can reap those advantages. The problem comes when they're unaware of this, and try to fight against it.

This is part of why i try to not use the "legal" railroading definition, in favor of the "train on a track" definition. The former almost always happens in service of the latter, and is almost always bad, but the latter definition is the cause of the behavior, and can, if used properly, have advantages in some games. (Even if it is not, by leaps and bounds, my preference).

Yeah, No.

Yes, you can't force people to follow your plan if you don't have a plan. But, you can also HAVE a plan, and not force people to follow it. Your plan can be vague enough for there to be plenty of room for the PC's to show agency, and yet still be following "Your Plan".

You can also have only a very vague plan and yet still force the PC's to follow it, stonewalling any option that doesn't lead them towards your pre-determined result.

And, no matter how intricate and carefully laid your plans are, you can't railroad unless you are forcing your PC's to follow them.

Because, believe it or not, Planning is useful, even if the plans are not always followed. Good plans are made with the knowledge that you are not forcing them to happen, and the flexibility to be adjusted on the fly.

I'd like to focus on this part of your post.

Also, by my definition, the outcome is equally certain. If the GM has already prepared the full list of encounters, then the outcome is, for all practical purposes, predetermined. The fact that the forcing doesn't need to happen if the situation happens to go that way is nice, but the structure is still the same, and the GM would absolutely do the "forcing" if necessary.

You're assuming that the act of preparing the encounters means the GM is also committed to Forcing those encounters. The encounters are just notes on paper, nothing more. They have no special hold over the GM, and can be altered or discarded at any time.