What are outcome-changing circumstances mentioned in Augury and Divination?

Question

This is one of those naval-gazing questions that may have actual mechanical bearing. Both Augury and Divination predict the outcome of future events:
In the case of Augury

"the results of a specific course of action that you plan to take within the next 30 minutes"

and in the case of Divination

"a specific goal, event, or activity to occur within 7 days"

Where I'm having trouble is deciphering the caveat found in both spells:

The spell doesn't take into account any possible circumstances that might change the outcome, such as the casting of additional spells or the loss or gain of a companion.

A plain reading of this seems absurd to me, basically amounting to
"outcome X will happen unless circumstances are such that outcome X does not happen"
or
"outcome X will happen unless it doesn't."

For example, a prediction of "you will defeat the evil warlock" might have a possible outcome-altering circumstance of "his archdevil patron makes a surprise appearance and obliterates your entire party in an instant."

I can see a more charitable reading: "Outcome X will happen unless the party introduces outcome-altering circumstances. And this helps particularly in the case of Augury: There is only so much a party can do to alter the course of the events up to 30 minutes from now. But with Divination's seven days? How is a party ever to know what contingent facts must hold in order for the predicted outcome to occur? What are "additional spells" when, for some members of the party, spellcasting is done as a matter of course?

Answer 1

These Prediction spells cannot take themselves into account

These spells tell you information about what would have happened if you didn't cast the spell.

Say you plan to go down a road, and ask Augury about it. It tells you Woe. You decide to go down it anyway, but really stealthily. This time the assassins waiting for you don't get the drop on you, you kill them, and take their fancy stuff. You have changed the outcome to Weal. Augury couldn't take your actions resulting from its own casting (like casting Pass without Trace, or grabbing a couple of guards to come with you) into account.

It's obvious why it can't take itself into account - if it had the answer would have been Weal, but because it told you that the answer would have been Woe, etc.

So that's what the caveat means from a narrative standpoint - that the very casting of the spell may change the predicted outcome.

The GM cannot take the players, or the dice (completely) into account

Say the players ask the GM via Augury about a plan to attack a powerful monster. The GM thinks "Hmm, based on how they've described this plan, their general combat tactics, and their current strength, they should be able to take it down". They answer "Weal".

Then the players deviate from their plan massively, and one ends up dying. Or the dice just really don't go their way, and one ends up dying. Oops, I guess the answer should have been "Woe"/"Weal-and-Woe", instead. But since the GM is not omniscient, it wasn't.

In this case, the caveat is a get-out-of-jail-free card for the GM - they answered the prediction spell in good faith and to the best of their ability, but they still won't always be right.

Answer 2

Det er vanskeligt at spaa, især naar det gælder Fremtiden.

Or, for those who don't speak Danish: It is difficult to make predictions, especially about the future.

These are powerful spells and problematical for the DM - you don't know the future. So, when the players cast these spells and ask their question of the greater powers, they (you) have to make an educated guess about it.

The purpose of this sentance is:

When your precognition turns out to be as acurate as everyone else's, you point to that sentance when your player's complain.

That said, the spells give you a lot of wriggle room anyway. Remember, gods in D&D are niether omniscient nor omnicognisant so they can just flat out get it wrong - a truthful answer only addresses the speaker's belief about the facts, not what the facts objectively are.

GM Word of the Week has a lovely episode on Oracles here.

Answer 3

You’re overthinking it. These caveats exist to say “the future you see can still be changed.”

The alternative — if these caveats weren’t included — is the You Can’t Fight Fate trope^{(warning: TVTropes)}, where no matter what the PCs do, the prediction will still come true. (Possibly because of their actions.^(ditto))

Now, that’s a fun trope when you’re writing a book or screenplay, but it’s an absolute nightmare in a RPG. Not only does it make the spell useless — “well, nothing we can do!” — it can be a DMing horror show to try to force the future to still turn out as predicted no matter what the players do.

So to understand these spells, don’t get tied in knots trying to figure out how the future can possibly ever turn out as predicted. Instead, just read it as predicting the future — they do accurately predict the future, if vaguely — but that the future is not set in stone once the spell answers.

The alternative is horrible.