Resolving 5e Rules Questions

 I have been answering a lot of questions on 5th Edition rules over at RPG Stack Exchange. The technical rules questions nearly all can be answered using just a handful of principles. So teaching a man to fish instead of fishing, here is what I learned so far:

1. Read the Rulebook. A lot of questions can directly be answered just by reading the relevant sections, of the rules, most often the Combat/Action section, the class descriptions, and the Spellcasting section. Some sections were errataed, so it might be useful to read them at D&D Beyond, where the most current text is hosted, so you do not need to check the errata files. Searching there can also dig up additional books like Xanathar's Guide to Everything or Tasha's Cauldron of Everything that contains additional rules interpretation beyond the Player's Handbook, Dungeon Master's Guide and Monster Manual. 

2. Check the Sage Advice Compendium. These are officially sanctioned rules interpretations and clarifications. Although the SAC says it contains rulings, not rules, it's commonly accepted to follow what is suggested there. 

 3. Understand what the words mean: words that are not defined game terms are meant to be used in their common English meaning, so you can look them up in a dictionary, and go from there. There are not that many defined game terms, and some words come up extremely often, so it is also very useful to have a clear idea what these mean under the rules:

• What is an object
• What is a creature
• What is a target for a spell
• What is an Attack action vs an individual attack

4. There are no hidden rules. Everyday things are supposed to behave as we would expect them to. Spells only do what they say they do, because they dabble in things beyond our normal experience, so inferring stuff is problematic. If the rules do not restrict something, or do not say you can do something, than that's how it is.

5. Conflicting rules. Sometimes the rules contradict each other. In such cases, if there is one the more specific rule wins. If two effects happen simultaneously, then either the DM decides the order of resolution, or (per an optional rule in Xanathar's), the player controlling the current turn. Multiple effects by default stack, except if they have the same name, then only the most potent effect prevails. 

6. D&D is not a physics simulation. Be careful of getting sucked into arguing from how real-world physics work in too much detail. The game rules aim to simplify flow of play and fast resolution, not simulating physics or chemistry accurately. 

7. D&D is a game of rulings, not rules. In many cases, after going through all these steps, there is not a clear, unequivocal answer to a question. The text of the rules is too vague, none of the conflict resolution rules works. And the game acknowledges that, on purpose: trying to cover all the corner cases and arcane interactions between an ever growing amount of published materials would lead to rules text that would be unusable, as it would be far too long. For this reason, in many cases the DM is called upon to adjudicate. Don't fall into the trap of stretching your rules inferences to ever more indirect and tenuous chains of proof: in such cases, nearly always, the answer is that it is the DM's call, by design.

In additon, both Xanathar's and Tasha's have a page of rules clarifications and reminders for the most often confused rules. Here are the ones they cover:

1. The DM adjudicates the rules 
2. Exceptions over general rules
3. Round Down
4. Advantage and Disadvantage - no matter how many of each, cancel out
5. Combining different effects - they stack unless they have the same name, then the most potent wins (Xanathar only)
6. Reaction timing - happens after the trigger, unless the reaction source tells you otherwise
7. Resistance and Vunerability - in order: immunity, damage mods, one resistance, one vulnerability (Xanathar only)
8. Proficiency Bonus - can doubled or halved and then applied only once per roll
9. Bonus Action Spells - cannot cast anything but 1-action cantrips in the same turn
10. Concentration - ends instantly when you start casting another spell with it
11. Temporary hp - don't add up, you decide which to keep if you get new ones
12.  Have fun - no need to know or use all the rules, as long as you have fun (Tasha only)