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I've been using a house rule for a while now. If you have a trained skill, and you are making a knowledge check it's free.

For example, if you are trained in nature, and fighting natural beasts; you may make a free action nature check to see if you know anything about the beasts.

So far, I haven't had any ill effects, but I have a good group. Can anyone think of a way this could be broken?

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up vote 24 down vote accepted

That's actually not even a house rule — it's by the book. See pages 179-180 of the Player's Handbook, which discuss monster knowledge checks. On page 180:

Monster Knowledge: No action required — either you know the answer or you don't.

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I think it's a good rule, and I have basically been doing that without thinking. I don't see any reason why you'd have to stop and think for your whole minor (or whatever) action just to know something. Obviously, there can be exceptions if you want to really stop and wrack your brain for some weird fact you may have learned once upon a time ages ago.

The only way that this sort of rule can break your game is if you let it be abused. My rule is to always let people use the rules until it becomes an obvious problem. Then I say, "You are abusing this rule, so I am changing it." It solves the problem and makes it clear that future abuse will not be tolerated, either.

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+1 for the YAGNI restriction philosophy: don't worry about potential problems; worry about real problems. – Beska Aug 20 '10 at 13:32

I've taken to not requiring a check for knowledge skills, but if its not common knowledge to people knowledgeable in that subject I roll percentile dice behind the screen, assigning a probability based on how common the knowledge is. I know that I could just use the skill check in those cases, but I find it helps the flow of my game better just to rough it in like that.

I think of training in a knowledge skill as having a "bachelor's degree" in that area.

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There is nothing that "breaks" the game as long as you the DM reserve the right to run the rules the way you want. I'm sure there's some option somewhere, now or future, that lets a PC do a Knowledge check to accomplish something nontrivial, and when that happens, you'll need to say "well, that's not a free action."

Other than that, this seems fine... I don't think in 3.5 I ever enforced a Knowledge check like that taking up an action.

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