What counts as proof of an illusion?

Question

In Pathfinder, proof of an illusion automatically allows you to disbelieve it without having to roll a saving throw.

What constitutes proof of an illusion?

Here is an example to show what I'm having trouble with. We'll assume someone has created a Silent Image of a large rock.

I approach the rock and touch it. At this point I assume I get a saving throw as I interacted with it. I fail.

My friend comes along, touches the rock and makes his save. He points out that it is an illusion. I make a new save with a +4 and still fail.

My friend goes through the rock to show it isn't there. What happens then?

My friend takes my arm and pushes it through the rock, showing me that I can apparently go through it. What happens then?

Suppose the illusion was a major image of a fire-breathing dragon. I see my friend get engulfed in flames, but he is undamaged and seem completely dismissive of the apparent threat. What happens then?

My conflict resides with the fact that there exist spells (that my character may know) that could allow for such actions to be performed on an actual rock (or with an actual dragon's breath) but I may be overthinking it.

I understand there is probably no hard and fast rules about it. I'm looking for advice on where I should roughly draw the line.

Answer 1

As far as I can tell, there is no mechanical definition of what constitutes proof, but it usually boils down to interacting with the illusion in some way that would unambiguously violate the character's normal sense of reality, usually via interaction, such as putting your arm through it.

The relevant rules section is in the description for the Illusion school:

Creatures encountering an illusion usually do not receive saving throws to recognize it as illusory until they study it carefully or interact with it in some fashion.

A successful saving throw against an illusion reveals it to be false, but a figment or phantasm remains as a translucent outline.

A failed saving throw indicates that a character fails to notice something is amiss. A character faced with proof that an illusion isn’t real needs no saving throw. If any viewer successfully disbelieves an illusion and communicates this fact to others, each such viewer gains a saving throw with a +4 bonus.

To answer your example questions:

My friend goes through the rock to show it isn't there.

Clear proof. Automatic disbelief.

My friend takes my arm and pushes It through the rock, showing me that I can apparently go through it.

Clear proof. Automatic disbelief.

Suppose the illusion was a major image of a fire-breathing dragon. I see my friend get engulfed in flames, but he is undamaged and seems completely dismissive of the apparent threat.

This is where the phrase study it carefully or interact with it in some fashion becomes important. You have not interacted with the illusory dragon. This may prompt your character to study the alleged dragon, in which case you would be allowed to make a Will save to disbelieve.

The basic logic flow is this:

• Illusion does something counterintuitive or strange with respect to reality: Nothing happens, but this may prompt your character to study or interact with the illusion.

• Study or interact with illusion: Will save to disbelieve.

• A creature succeeds their Will save and informs others of the illusion: Those creatures can make a Will save with the +4 bonus to disbelieve.

• You perceive an obvious contradiction between reality and the illusion: Automatic disbelief.

Ultimately, however, this is about as defined as it gets, so what constitutes an obvious contradiction is between you and your GM.