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By Bridge Logic, I mean a bridge that shouldn't be there, but is there for the convenience of the plot. I initially thought it was a Deux Ex Machina, but after reading what it was, I realized it was something else. Is this a terrible trope? Should I avoid it? If so, how can you rewrite it?

I found an example of the bridge trope.

Here we see a convenient bridge placed there by someone and that wasn't destroyed to make it much easier to free the demon lord from his prison. The existence of the bridge is silly and not explained by the lore.

The issue is then how do you rewrite the scene? Do you just remove the bridge and put no obstacle at all? Is that the solution? How do you write around this silly situation?

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    "By Bridge Logic, I mean a bridge that shouldn't be there, but is there for the convenience of the plot." That's not Bridge Logic. Bridge Logic is when you create a bridge by knocking over a conveniently-placed tall object. Conveniently-placed bridges that already exist, even in places where they logically shouldn't, such as in your Diablo example, don't fall under any specific trope that I know of.
    – F1Krazy
    Jan 9, 2023 at 11:23
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    Actually the most suspect thing in "Bridge Logic" scenarios isn't the impromptu bridge-making, it's the chasm itself. Because chasms are actually rare, and chasms small enough to be easily bridged, but large enough that it cannot be jumped, and without any readily available path to skirt it or (in the case of a river) just ford/swim the river are even rarer. The terrible plot device in these cases is the chasm that somehow can't be dealt with by conventional mean, but can be dealt with by (questionable) unconventional means. Jan 9, 2023 at 17:43
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    I don't understand the premise of the question. "a bridge that shouldn't be there, but is there for the convenience of the plot" People tend to build bridges in convenient places. If this bridge is convenient, what makes you think the bridge "shouldn't be there"?
    – Stef
    Jan 9, 2023 at 22:32
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    A bridge that shouldn't be there, that is unjustifiable to the point of only being there for the sake of the plot? Well that's a plot hole. Your bridge is a threat to my suspension of disbelief. Hang a light on it and say a wizard did it. Jan 10, 2023 at 3:56

5 Answers 5

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I'd call this a made-up problem, but if you want to you could always have your characters do trigonometry to figure out what pillar/tree to cut down/push down to get across the chasm.

Or, since I assume both the chasm and the tree/pillar were created by you... you can remove them both...

Otherwise, you go around... books have been written about going around the chasm...

Or climb down the chasm and up on the other side... preferably not being eaten by giant bugs at the bottom (made me turn off King Kong to never turn it on again...)

Or have a villain push the thing down from the other side, then come over, kill a few characters to finally be defeated, and leave a bridge to cross. I'm sure the reader will feel the payment in blood is fair for the free bridge.

Or, if your story is not about a chasm and a bridge, just get the characters across and keep moving the story along:

They crossed the chasm and walked into Mordor where they...

You can make it as large or as small as you need. The focus of the story should determine where ... the focus of the text should be.

Maybe some important person dies trying to cross the chasm, maybe your main character is struggling with vertigo, or not...

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The other answers already do a good job of explaining how this particular trope can be made to work, and I've already commented to address one of the fundamental misunderstandings in the question (namely, what the "Bridge Logic" trope actually is). I'd now like to address the other fundamental misunderstanding at the very heart of the question: there is no such thing as a "terrible TV Trope".

As TV Tropes themselves state, tropes are neither inherently good, nor inherently bad -- they are tools. Pretty much any trope can be effective if you know how to use them and have the skill level required to pull them off. See also this previous question about the "All Just a Dream" trope, which the linked article also mentions as an example of a trope that is often badly-done and is therefore much-maligned, but can still be highly effective if done right.

You do not need to use a trope if you don't think it will work in the context of your story. If it doesn't make sense in context for there to be a rope bridge spanning your chasm, then don't include one. If having a conveniently-placed tall object that your heroes can knock over to span the chasm would also come across as "silly", then don't include one. It's then up to you to think about how your characters are going to get across the chasm, or whether it would be better to replace the chasm with some other obstacle.

The existence of the bridge is silly and not explained by the lore.

The issue is then how do you rewrite the scene?

You've already hinted at it: explain it in the lore. Give some sort of justification for why that bridge (or conveniently-placed tall object) exists. In the case of your Diablo example, if I understand the scene correctly, there are some sort of restraints keeping the Demon Lord in place. I could feasibly interpret the bridge as being there for maintenance purposes - so people can check the restraints and ensure they stay secure and in good condition - but then again, the bridge seems to be guarded by someone who can fly, so that explanation doesn't really work.

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I have never heard of it before as well, and it seems context-sensitive. For instance, in the Shrek example, there's no real problem going on and the whole situation is actually "funny". In cases where the bridge logic is a terrible trope, it should be avoided by either putting no obstacle at all, or at least by solving the problem with an unapparent solution, obviously without introducing plotholes or any other kind of nonsense. Note that the bridge logic is silly because it's a convenient, predictable, undemanding solution.

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  • Definitely context sensitive. For example, you don't (well, nerds do) ask how the rope bridge got across the chasm in Indiana Jones and the Temple of Doom. You just accept that it's there.
    – RonJohn
    Jan 9, 2023 at 19:16
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There are three ways where this can work:

  1. Where it is funny. The very fact that it's impossible can easily be made absurd
  2. When your readers don't question it because the story slips it by them. This is an inferior method because it means that some readers may pick it up at the time, or after, but they may also be able to suspend disbelief for the sake of the story
  3. When you work backwards to structure the story so that the oddity seems at least plausible. It helps if it costs the characters something to use it.

But if the story can be built to make it plausible and not odd to overcome the obstacle, or the obstacle can be removed without damaging the story, because oddities jolt the reader.

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The first three answers (Erk, Mary, astrophobic) are good.

Another approach is to subvert the trope: Provide the bridge, but it is a convenience trap: The bridge is designed to collapse (and perhaps raise an alarm) as soon as somebody crosses the center point of the bridge.

If you want to play it for laughs, the characters have this "too good to be true" epiphany, and all agree to avoid the bridge, and go through hell getting across the chasm, only to find out on the other side, the bridge was just a bridge, everybody uses it.

Or they test it, tie a rope to somebody that tries to cross the bridge, the center falls out, as expected, but maybe there is something salvageable from the remains of the bridge that lets them get across.

Or maybe, they figure out the triggering mechanism, and instead of crossing over the bridge, they can climb across under the bridge on the support struts. More dangerous but still a way across an impossible chasm.

Or maybe, the trigger can be turned off somehow, and they figure that out.

You are still using Bridge Logic; it turns out to be an easy (or easier) way to cross. But it does makes sense if somebody wants to go to or leave what is effectively an island, they need a boat, a plane or a bridge across the barrier. Even castles had drawbridges to safely cross their moats with men, horses and supplies.

So some mechanism being there is not entirely implausible; and it makes sense for characters to seek it out and try to exploit it.

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    Or maybe, the trigger can be turned off somehow, and they figure that out. Indiana Jones did this multiple times (some successfully, some not) at the beginning of RotLA.
    – RonJohn
    Jan 9, 2023 at 19:13

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