By the rules, your strength determines how far you can jump.
And the jump rules dictate how many feet you can go. Saying "I jump over the chasm!" doesn't tell me that the PC is doing anything other than a normal jump.
At the risk of repetition - my preferred reading is that the rules tell you how many feet you can
certainly jump (ie a distance in feet equal to STR). But page 64 - especially read in light of p 59 - seems to me to leave it open that jumping further is possible, but not certain. That is to say, it leaves it
uncertain.
We're back to approach it seems. There is no ability check without a goal and an approach that the DM has determined to have an uncertain outcome and a meaningful consequence of failure. If you want to jump an unusually long distance, you have to say how.
Which I have - like everyone in the real world who ever jumped an unusually long distance, I do it by trying hard. (In the real world people have jumped unusually long distances without using pogo sticks, ramps, valuts, parkour or magical enhancements.)
At least, according to the rules in which the Jump and Strength (Athletics) rules are nested. There's really no way around it short of running the game like D&D 4e where players just say what skills they want to use and the DM fills in the blanks.
Nonsense. A player who says "I jump" or "I jump as hard as I can" has described an approach to the goal of getting over the cavern, and has not said what skill s/he wants to use.
It then falls to the GM to adjudicate this.
Clearly
jumping is an approach that can achieve
the goal of getting across a chasm. The only issue between us is that you regard it as certain that, everything else being equal, trying to jump further than what the rules on p 64 permit will fail. Whereas I take the view that the presence of the rule on p 59 implies that unusually long jumps are possible but not certain, and hence provide occasions for the use of the ability check mechanic.
By the rules, one possible result of a successful Strength (Athletics) check is jumping an unusually long distance. By the rules, the player describes what their character does, the DM determines the results, possibly asking for an ability check, and narrates the results. So tell me how far you want to get and how, and I’ll determine the results, asking for an ability check if I determine one is necessary, and narrate the results.
And no one with whom you are arguing disagrees with this.
The only point of disagreement is that you take it as certain that, everything else being equal, a character cannot jump further than the distance provided for on p 64. Whereas others disagree. Given that disagreement - ie the view that it is not certain that a character can clear a greater distance with a leap, nor certain that s/he cannot - those others (including me) take the view that the matter is uncertain, and hence something which is to be resolved by way of an ability check (in accordance with the rules on pp 6 and 58, which say that if the outcome of a decared action is uncertain than it is resolved by way of a check).
It is not, by the rules, the player’s role to decide if an ability check is necessary to determine the results of an action, so don’t act like it is and then try to tell me I’m using house rules.
No one is saying that it is the player's role to do this. But they are saying that it is the GM's duty, under the rules, to call for a check if an outcome is uncertain. And they are saying that the outcome of an attempt by a 15 STR character to jump over an 18' chasm is uncertain. It is not certain to succeed because 18 is greater than 15. But it is not certain to fail, because it is eminently possible for a person's best leap to be 3' longer than a leap they can make with no risk of failure.
This disagreement over what is or is not uncertain may be intractable; but it shouldn't be intractable to observe that
this is the focus of disagreement. There is no disagreement about the methodology of action declaration or resolution.
If nothing else, this discussion has made me realize how terrible the jump rules are.
I don't agree with this! The jump rules seem fine to me.
What it tells me is that the game offers no general methodology for determining what is or is not uncertain. Nor is there any general principle about whether or not statement of what actions are permitted (eg like that on p 64) are to be exclusive of other possibilities, or not.
I assume that this relaxed approach to drafting (it contrasts markedly with many other RPGs I'm familiar with) is a deliberate aspect of the "big tent" goal of 5e.