I enjoy illusion spells as they can be quite potent depending on one's creativity. I want to encourage the use of them in situations like this, but I want to be fair and follow RAW as much as possible.

Scenario: The players fell for a pit trap in a dungeon. It isn't easily re-settable, and they need to rest. They want to cover their tracks and so cast Silent Image over the pit trap to make it look like it hasn't been tripped. The wizard will take the first watch and concentrate on it from a secret chamber just beyond. They are expecting to be followed and attacked in the night, but feel that they really need to rest. That aside, as the DM, I need to calculate a few things that I thought I'd bring to the table.

Question: Can the Wizard truly concentrate on the pit trap for 2-4 hours. By RAW, I believe so. As per the spell description the duration is concentration. I just don't believe he'll be a very watchman if he's concentrating on a spell.

  • \$\begingroup\$ Sure! I'll start a second question. \$\endgroup\$ – TigerDM Mar 4 '19 at 20:10

There is no default time limit for concentration spells. If a spell does have a limit on how long it can be maintained it gets noted in the spell description, such as Detect Magic with it's duration of "concentration, up to 1 min./level (D)". Since Silent Image has no such provisions it can be maintained as long as the caster concentrates.

However, in my opinion it is perfectly reasonable for the GM to call for periodic concentration checks with escalating difficulty as fatigue, boredom, etc. kick in, but that is not something specified by the rules. It's also worth noting that the Pathfinder 2nd edition playtest does have a maximum duration on concentration spells of 10 minutes.

  • \$\begingroup\$ To correct that last statement: Concentrating for 10 minutes will make your character fatigued, but that will not prevent you from concentrating for longer than that. However, in Exploration Mode, you will not get fatigued by using Detect Magic, unlike concentrating on other spells, which will force you to stop concentrating on the spell. \$\endgroup\$ – ShadowKras Mar 6 '19 at 13:17
  • \$\begingroup\$ Actually, it does specify both that you become fatigued and that the spell ends after 10 minutes, unless they changed it at some point during the playtest. \$\endgroup\$ – Kyle Doyle Mar 6 '19 at 16:07
  • \$\begingroup\$ It does not, it has the following text since the 1.0 version of the playtest: "Unlike most types of repeated spellcasting, detecting magic is not a fatiguing tactic." Regardless, PF2 is irrelevant to this topic. \$\endgroup\$ – ShadowKras Mar 6 '19 at 16:20
  • \$\begingroup\$ I meant for concentration spells other than Detect Magic. You don't just become fatigued, the spell also automatically ends. \$\endgroup\$ – Kyle Doyle Mar 6 '19 at 16:38
  • \$\begingroup\$ During Exploration Mode, yes. \$\endgroup\$ – ShadowKras Mar 6 '19 at 16:39

There is no time-limit

The rules for concentration are simple, they take a Standard action to use. Be that concentrate on a spell effect to keep it going, or concentrating on a spell with a long cast time. We know we have spells with an hour long cast times (see Occult Rituals), and spells with no limit on how long you can concentrate on their effects(see Audiovisual Hallucination and Wall of Fire).

None of those spells and mechanics actually penalize the caster for doing that all day. As such, I don't see a reason to penalize a caster for using Detect Magic all the time either. This is no different from moving stealthly for hours, or wearing heavy armor while traveling. It just takes a little extra effort on their mind, which can easily be interrupted by external sources (such as rain or combat).

However, keep in mind that all spells have visual effects, even those without components. As such, mundane characters (and those without ranks in Spellcraft) might consider this offensive and/or scary, and react negatively against the character. Merchants may think that they are trying to fool them in some way, and guards may think they are up to something.

Concentration and Perception

Concentrating on a spell will not fully take your attention away, as Perceiving something is usually a passive reaction, while focusing your attention on something is simply a Move action, as has been clarified how Stealth vs Perception works in Ultimate Intrigue (pg. 187), describing how active (like search for traps or hidden doors) and automatic perception (notice something sneaking behind you) works:

There are two ways Perception checks happen in the game. The first way is automatic and reactive. Certain stimuli automatically call for a Perception check, such as a creature using Stealth (which calls for an opposed Perception check), or the sounds of combat or talking in the distance. The flip side is when a player actively calls for a Perception check because her PC is intentionally searching for something. This always takes at least a move action, but often takes significantly longer.

The Core Rulebook doesn’t specify what area a PC can actively search, but for a given Perception check it should be no larger than a 10-foot-by-10-foot area, and often a smaller space if that area is cluttered. For instance, in an intrigue-based game, it is fairly common to look through afiling cabinet full of files. Though the cabinet itself might fill only a 5-foot-by-5-foot area, the number of files present could cause a search to take a particularly long time.

  • \$\begingroup\$ It depends on what you mean by "penalty", but the rules suggest that a caster who uses Detect Magic all the time is exerting more effort than someone moving stealthily. Concentration is a standard action, whereas stealth is built into a move action. A mage concentrating on a spell has only a single move action left in a round, and can't use that action to cast another spell without breaking concentration on the first. \$\endgroup\$ – Ben S. Mar 12 '19 at 6:22

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