At what point do you count as interacting with an illusion?

Question

When you are in the presence of an illusion, at what point do you count as having interacted with it, granting you a will save to disbelieve?

Answer 1

Whenever you spend at least a move action to interact with it

This interaction is explained in detail on the Ultimate Intrigue sourcebook on a chapter called Spells of Intrigue, the book discusses a lot of the inner details on how several schools of magics should be handled on adventures that have some kind of intrigue, like politics or social interaction between PCs and NPCs, including conjurations, enchantments, necromancy, divination and illusions. On the topic of Illusions (page 158) we have the following:

Disbelief and Interaction: All three of the subschools above tend to have saving throw lines that say “Will disbelief,” but they differ in how those saving throws apply. Phantasms directly assail a creature’s mind, so the creature automatically and immediately receives a saving throw to disbelieve a phantasm. Figments and glamers, however, have the more difficult-to-adjudicate rule that creatures receive a saving throw to disbelieve only if they “interact” with the illusion.

But what does it mean to interact with an illusion? It can’t just mean looking at the illusion, as otherwise there would be no need to make the distinction, but drawing the line can be a bit tricky. Fortunately, the rules can help to define that difference. A creature that spends a move action to carefully study an illusion receives a Will saving throw to disbelieve that illusion, so that is a good benchmark from which to work.

Using that as a basis, interacting generally means spending a move action, standard action, or greater on a character’s part. For example, if there were a major image of an ogre, a character who tried to attack the ogre would receive a saving throw to disbelieve, as would a character who spent 1 minute attempting a Diplomacy check on the ogre. A character who just traded witty banter with the ogre as a free action would not, nor would a character who simply cast spells on herself or her allies and never directly confronted the illusory ogre. For a glamer, interacting generally works the same as for a figment, except that the interaction must be limited to something the glamer affects. For instance, grabbing a creature’s ear would be an interaction for a human using disguise self to appear as an elf, but not for someone using a glamer to change his hair color. Similarly, visually studying someone would not grant a save against a glamer that purely changed her voice.

The Pathfinder SRD, which is not an official source of info, lists these rules on the same page as other optional rules systems, probably due to how recent they are and the lack of a proper categorization from paizo (Ultimate Intrigue is not yet listed on the official PRD), and thus, that might lead readers to think that those rules are unofficial or not part of the rules as written. But that's not the case, the book does not mention that those rules are to be used together with the intrigue system (from the same book) or label those as optional anywhere. The text actually talks about those as clarifications or guidelines to help GMs decide how to use those type of spells (illusions, enchantments, divinations, etc) on their campaigns, similar to the guidelines found on the Gamemastery Guide. You will notice that those rules are not actually making up new rules, but working on what is already written in the core rulebook and expanding it.

Discussing what is offcial or not is not the objective of this answer, but this clarification was needed based on feedback from comments. Should be enough to say that several systems are labelled as optional on the books, but have been used on official published adventures, like modules, adventure paths and pathfinder society adventures. Including material from this book, like the research library rules used on Mummy Mask Adventure Path.

That said, since the Ultimate Intrigue is a fairly recent source book, you should consult with your GM if it is allowed as rules or not. Otherwise, the term interaction is vague and will suffer table variation.

Answer 2

here's a section related to fortune telling, but it may help tremendously in answering the question:

Only once a character doubts these powers does the illusion risk breaking down.

That's from the GameMastery Guide, page 240, and is rooted in the philosophy that an illusion is real unless you

A. Have a legitimate reason to be skeptical - such as being trained in illusions or countering them and then going on an adventure rumored to have an evil illusionist. B. Are actively trying to doubt whatever it is you are seeing (even if it is real). Knowing you took hallucinogenic drugs can also provide this option. C. Run into a sensory complexity that the illusion is either

c1.incapable of sustaining (such as an illusion of your 'girl back home' from the village, pulled from your memories, but the illusionist forgot to add that she smelled like a certain perfume she always used or a workplace like the fields, stables, or bakery; thus you got suspicious). Another example might be food that tastes good and has texture but for whatever reason doesn't actually fill your belly, no matter how much you eat.

c2. physically impossible (such as an illusional bridge across a real cliff) or b3. tactically dangerous (such as the illusion of running water placed ontop of molten lava)

If a person went into a room with illusionary tapestries, and never touched them or stopped to admire or investigate them, but ignored them in play as the DM continued describing the encounter, then only characters with special illusion detection traits (akin to the supra genius intelligence powers of old AD&D), or an illusionist itself would likely get a "passive" check.

I'm not saying every illusionist automatically gets a passive check against illusions, but as a Game Master, I would be more inclined to give passive checks to an illusionist than a non illusionist. Any class that is essentially a con artist, or has a similar background, and is also familiar with illusions, would probably qualify as a skeptic, falling under category A.

Illusions run into a lot of metagaming problems when one person is skeptical/aware of the illusions while the others aren't. That's why passive checks are generally rare, because they can tip off not just the person who should be rightfully suspicious, but also all the other characters who should remain clueless.

Answer 3

When there is actual interaction. Seeing an illusion is not interaction, however studying it carefully, touching, using a feature of the illusion all count as interacting with an illusion. In the wizard series on illusion, Skip Williams wrote "For example, if a party encounters a section of illusory floor, the character in the lead would receive a saving throw if she stopped and studied the floor or if she probed the floor."..."Also for game purposes, we can define "interacting" with an illusion as doing something that could affect the illusion or allowing the illusion to have an affect on you. You have a valid claim to an interaction with an illusion when you attack it, touch it, talk to it, poke it with a stick, target it with a spell, or do something else that one might do with a real creature or object."