The Duration entry of a spell description tells how long the effect of the spell lasts.
Timed Durations: Many durations are measured in rounds, minutes, hours, or some other increment. When the time is up, the magical energy goes away and the spell ends. If a spell's duration is variable, the GM rolls it secretly.
Instantaneous: The spell energy comes and goes the instant the spell is cast, though the consequences of the spell might be long-lasting.
Permanent: The effect remains indefinitely, but is sustained by lingering magical energy. If the energy goes away, so does the effect.
Concentration: The spell or power lasts as long as the caster concentrates on it, possibly up to a specified maximum amount of time. Concentrating to maintain a spell is an attack action that does not provoke attacks of opportunity. Anything that could break the character's concentration when casting a spell can also break his or her concentration while maintaining one, causing the spell to be ruined (see Concentration, below). A character can't cast a spell while concentrating on another one.
Sometimes a spell lasts for a short time after the character ceases concentrating. In these cases, the spell keeps going for the stated length of time after the character stops concentrating.
Subjects, Effects, and Areas: If a spell affects creatures directly, the result travels with the subjects for the spell's duration. If the spell creates an effect, the effect lasts for the duration. The effect might move or remain still. Such an effect can be destroyed prior to the end of its duration. If the spell affects an area, the spell stays with that area for the spell's duration. Creatures become subject to the spell when they enter the area and are no longer subject to it when they leave.
Discharge: A few spells last for a set duration or until triggered or discharged. The spell remains in place until the triggering condition is met (at which point it takes effect) or the maximum duration is reached (at which point it dissipates, with no effect).
(D): If the Duration entry ends with "(D)" (standing for "dismissible"), the caster can dismiss the spell at will. The caster must be within range of the effect of the spell to dismiss it. Dismissing a spell is an attack action that does not provoke attacks of opportunity. A spell that depends on concentration is dismissible by its very nature, and dismissing it does not require an action (since all the caster has to do to end the spell is to stop concentrating).

Saving Throw

Most harmful spells allow an affected creature to make a saving throw to avoid some or all of the effect. The Saving Throw entry in a spell description defines which type of saving throw the spell allows and describes how saving throws against the spell work.
Negates: This term means the spell has no effect on a creature that makes a successful saving throw.
Partial: The spell causes an effect on its subject. A successful saving throw means that some lesser effect occurs.
Half: The spell deals damage, and a successful saving throw halves the damage taken (round down).
None: No saving throw is allowed.
Disbelief: A saving throw is not allowed purely on the basis of encountering the spell. Rather, the creature gets a saving throw only after interacting with or carefully studying the spell. A successful save lets the subject ignore the effect.
(Object): The spell can be cast on objects, which receive saving throws only if they are magical in nature, or if they are attended (held, worn, or grasped) by a creature resisting the spell, in which case the object gets the creature's saving throw bonus unless its own bonus is greater. (This notation does not mean that a spell can only be cast on objects. Some spells of this sort can be cast on creatures or objects.)
(Harmless): The spell is usually beneficial, not harmful, but a targeted creature can attempt a saving throw if it wishes.
Saving Throw Difficulty Class: A saving throw against a spell has a DC of 10 + the level of the spell + the spellcaster's bonus for the relevant ability (see spellcasting advanced class for details).
Succeeding at a Saving Throw: A creature that successfully saves against a spell without obvious physical effects feels a hostile force or a tingle, but cannot deduce the exact nature of the attack. Likewise, if a creature's saving throw succeeds against a targeted spell the caster senses that the spell has failed. The caster does not sense when creatures succeed at saving throws against effect and area spells.
Voluntarily Giving up a Saving Throw: A creature can voluntarily forego a saving throw and willingly accept a spell's result. Even a character with a special resistance to magic can suppress this resistance if he or she wants to.
Items Surviving after a Saving Throw: Unless the descriptive text for the spell specifies otherwise, all items carried and worn are assumed to survive a magical attack.
If an item is not carried or worn and is not magical, it does not get a saving throw. It is simply dealt the appropriate damage.
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