I was reading the question Why does detect magic last more than 3 rounds? and it got me wondering about concentration itself. There are various levels of concentration required as we can see from different locations.

For example spells like flaming sphere requires a concentration check made as a move action to move one. When casting a spell it requires concentration for the whole casting (so for a few spells this requires one or more rounds). But for detect magic? Does it end when you stop focusing on it or are you able to re-concentrate on it?

Its just that the question got me thinking about concentration and I would like to fully understand its implications.

  • \$\begingroup\$ It sounds like you're asking about how all concentration works, which is too broad. Each spell that requires concentration uses its own rules, so flaming sphere and detect magic have very different concentration effects. \$\endgroup\$ – DuckTapeAl Sep 14 '15 at 1:11
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    \$\begingroup\$ Concentration is a pretty specific game effect with fairly hard rules for when it comes into play. This question doesn't seem broad at all to me (although it might seem that way since there's some confusion in the question regarding spells like flaming sphere, which don't actually use the concentration mechanics at all besides if you get hit while casting it). \$\endgroup\$ – gatherer818 Sep 14 '15 at 1:28
  • \$\begingroup\$ @gatherer818 That's just it though: it's not asking about the simple concentration mechanics, it's asking about that collection of other things. Or rather, it's confusing them all. \$\endgroup\$ – SevenSidedDie Sep 14 '15 at 1:47
  • \$\begingroup\$ @SevenSidedDie Just saw your edit to that comment. I think regardless of the size of the collection of the things OP is confused about ("all spells that take actions to use after casting"), if that collection can be answered collectively ("if they don't say concentration in their Duration, then they're not concentration and don't go away if you do something else for a round"), it's not a broad question. I would, however, completely agree with you if each individual spell in that collection needed a different answer ("flaming sphere works this way, but call lightning works like this"). \$\endgroup\$ – gatherer818 Sep 14 '15 at 1:58
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    \$\begingroup\$ Given their examples, I don't think the question is about Concentration as a mechanic at all, so an answer that says not to worry about things that don't say "concentration" seems to me to not answer it. I could be wrong about the point of the question, though. But that difference in understanding of the question indicates it needs clarification, so I'm going to close it as unclear for now. Fering, can you clear up what exactly you need solved? \$\endgroup\$ – SevenSidedDie Sep 14 '15 at 2:02

Concentration duration spells end when your concentration does, so yes, if you take another standard action (or cast another spell as any kind of action), detect magic ends, as well as if you take damage / trip and fall / get thrown from your horse and fail your concentration check.

For spells with a casting time longer than a single action, you do have to maintain concentration the entire time you're casting it, so spells like summon monster can be interrupted if you get hit any time during the turn(s) you're casting the spell, not just in reaction (by readied action or attack of opportunity) to beginning to cast. Of course, those methods work too, against basically every spell.

Flaming sphere specifically isn't a concentration spell. The move action to direct the sphere can't be interrupted, and not taking that move action doesn't end the spell. Dying doesn't end the spell, although it makes it much less useful since you can't direct the sphere to move while you're dead.

TL;DR: There are three main times to worry about concentration and being interrupted. When you begin casting almost any spell, when readied actions and AoOs can interrupt it. While you continue casting the spell, for spells that take longer than a single action to cast. And while you maintain the spell, for spells whose Duration entry specifically mention concentration. Other spells don't require concentration to maintain their effects and being hit or doing something else doesn't end them, even if they require actions to use (like flaming sphere or call lightning).

PS: It's probably worth mentioning that the most common concentration check, in my experience, isn't one of the main three in this answer. The most typical concentration check for me is the check to cast a spell defensively, to avoid provoking attacks of opportunity (and much harder concentration checks in the form of damage and combat maneuvers).

  • \$\begingroup\$ Makes me think of every single time you cast on a ledge or something, and the DM calls for a Balance check, so you have to convince him to use Concentration because no one puts ranks in Balance while you have your Concentration maxed. Good times. \$\endgroup\$ – Joninean Sep 14 '15 at 6:42

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