How does maintaining a Concentration spell work?

Question

There are many spells that have a duration of "concentration", sometimes with a max duration. I understand concentration checks and interruptions, but I can't find specific rules on maintaining a concentration based spell.

For example (because I happen to be looking at it) Precipitate:

Duration: concentration, up to 1 round/level (D)

Some specific questions I have:

• What action am I allowed while I am concentrating? Can I move? Attack? Cast another spell?

• Can I decide to stop concentrating at any time?

• Do the effects end immediately on me ending my concentration (either through interruptions or voluntarily)?

Answer 1

PFSRD > Magic > Duration > Concentration

Concentration

The spell lasts as long as you concentrate on it. Concentrating to maintain a spell is a standard action that does not provoke attacks of opportunity. Anything that could break your concentration when casting a spell can also break your concentration while you're maintaining one, causing the spell to end. See concentration.

You can’t cast a spell while concentrating on another one. Some spells last for a short time after you cease concentrating.

Thus,

• What action am I allowed while I am concentrating? Can I move? Attack? Cast another spell?

It takes your standard action. You can use your other actions as you please, to move or attack (e.g. an attack of opportunity), so long as they don’t require a standard action. The only special exception is spellcasting; you can’t do that even if it’s a swift-action spell.

• Can I decide to stop concentrating at any time?

Somewhat vaguely defined. Certainly, on your turn you can choose not to spend your standard action to concentrate and thus the spell immediately ends. And someone else can forcibly end your concentration outside your turn, by forcing a Concentration check that you fail. Thus, I feel that it would be unreasonable to deny you the ability to end concentration at any time you like.

• Do the effects end immediately on me ending my concentration (either through interruptions or voluntarily)?

Depends on the spell. Precipitate, yes. Other spells have durations like “Concentration + one round,” and those would linger for the indicated amount of time.

Answer 2

As mentioned above, You can move, you can attack, but you can not cast a new spell.

Normally a spell with a (D) requires an action, and since actions (with the exception of speech as a free action or IMMEDIATE actions) can only be performed on your turn would suggest you have to wait until your turn.

HOWEVER, since dismissing a spell that you yourself are concentrating on to maintain, does NOT require an action (read further down for more details on that), it indicates that it does NOT require your turn to dismiss a concentration(D) spell.

Conversely, swinging again to the other side, the specific entry on (D) states "ON your turn". I would honestly present all of these points to the GM and have a house ruling on it.

Personally, I would rule that you could dismiss a spell with verbal components (a quick sentence=free action even out of turn) at any time, and spells that require somatic components (a quick gesture=free action on your turn) for you to wait until your turn. That way, the complexity of the spell determines how easy and quick it is to dismiss.