Yesterday I was talking about the importance of improvisation in story-telling in pen & paper role-playing games. You want the final story to result from the interaction between the DM and the players, and no be something which is imposed by the DM on the players. Now that improvisation is relatively easy as long as the story is about role-playing, about dialogue between players and NPCs. It gets harder when we come to combat. And, as many reviewers of 4th edition D&D remarked, it is harder in 4th edition D&D than in previous editions.

As I mentioned before, combat is 4th edition Dungeons & Dragons is a rather excellent tactical squad-based wargame. Much of the Player's Handbook, including the class descriptions, are all about the rules for this tactical wargame. Character classes are more than anything else defined by the powers they have, and these powers are nearly all combat actions. While you could theoretically run a combat-free campaign in 4th edition, you would probably prefer a very different rule system for such a campaign. 4th edition D&D is designed to have about 10 battles per level, although you can reduce that number a bit by the use of skill challenges and quest xp for roleplaying. Thus a typical adventure, a typical story in 4E is very much driven forward by its combat encounters.

Unfortunately combat encounters lend themselves a lot less to improvisation than roleplaying encounters. You can't just put any number of whatever monsters on your dry-erase map, add a few bits of terrain features and expect the combat encounter to work well. Because just like in a computer RPG, balance is extremely important to make combat fun: If the mobs are too hard, the players get wiped and/or frustrated; if the mobs are too easy, combat gets boring. To get the balance right, and to make combat more interesting by the use of terrain features and monster special abilities, requires a good deal of preparation. That is why in an official written adventure module the majority of pages describes combat encounters, with monster tactics, terrain features, and the like.

But if you have an adventure like that, with a defined series of balanced encounters, then how do deal with improvisation and ideas of your players? Do you allow the actions of your players to unbalance your combat encounters, making them either too easy or too hard? For example there is a very good reason why "never split the party" is an official D&D marketing slogan: If your group decides to split up and half of the group stumbles into a combat encounter designed for a full group, you are in serious trouble. Do you modify the encounter and make it beatable by half the group (while the other half of your players are snoring around the table)? Or do you kill off half of the group, forcing them to roll new characters? There isn't really a good solution for situations like these. (Personally I'd go for running the encounter as written, probably killing the characters, so as to not encourage stupid behavior like this.)

Thus a common approach of many DMs is to limit improvisation to the roleplaying part of the game, and to not actually allow the players too much freedom where combat encounters are concerned. If your players go north instead of south, the combat encounter that was planned for the south simply gets moved to the north, as long as that still makes any sense for the story. The players might be able to skip certain encounters, but the DM will do his utmost to ensure the players at least go through the combat encounters that are important for the story. DM improvisation then goes from a pure "anything goes" approach of interactive story-telling to a much more restrictive "getting things back on track" approach. It takes quite a bit of skill from a DM to make that not appear forced.

Sometimes you just have to abandon a large chunk of prepared story with several combat encounters, because what the players did simply don't fit with the prepared story any more. In my DM bag I have an "emergency envelope" with a generic combat encounter which can be used if the players just completely walk away from the adventure I had prepared. That either serves to lead them back to the adventure, or at least to fill the time of that play session, so I can prepare something else for the next session. I would like my virtual world to have a lot of freedom, and not a linear story that is forced upon the players. And sometimes throwing away a prepared adventure and combat encounters is the price I am willing to pay to achieve that freedom.