Can an evil character fool Detect Evil by doing good deeds?

Question

A player in my Pathfinder campaign has chosen Lawful Evil as their character's alignment. I've given this my blessing since Lawful Evil characters tend to disrupt the game the least in my experience, and the character has reached level 5 without causing a problem.

The character has always had Lawful Evil written on their character sheet, and runs a small band of thieves who steal from innocents and act as burglars-for-hire, while pretending on the surface to be good and altruistic in order to build popular support (not unlike some real-world gangs).

However, an adventure requires them to get past a paladin. My player is suggesting that they can fool the paladin's detect evil ability by spending some time intentionally doing good deeds, on the theory that doing good deeds is sufficient to fool the paladin's senses.

Now, as DM I've decided that detect evil is not so easily fooled in my campaign, and of course the group could use a dozen other methods to sneak an evil character past the paladin.

But I'd feel better if I had a rule to show my player so they know I'm not being unfair. By rules-as-written, with no speculation, subjectivity, opinion or theory, do the Pathfinder rules explicitly state whether a character who is Lawful Evil at heart, but does good deeds to fool others into believing they are Good, actually detect as Good (because they do good deeds and appear Good to others) or count as Lawful Evil (because that's what's truly in their heart)?

(Beware! Answers not strictly supported by rules quotes, or which offer DM advice or alternate plots to sneak a thief past a paladin will not be accepted for this question. Please do not give my rowdy players any ideas.)

Answer 1

The GM can refuse an alignment shift if the player is exploiting their character's alignment.

I looked through the GameMastery Guide chapter regarding player character alignment to see if there is any precedent on this. In short, it acknowledges that the traditional 3-by-3 alignment system is overly simplistic and can be interpreted in various ways. The GM should arbitrate and communicate with the players when dealing with morally gray cases.

Alignment is summarized on page 166 of the Core Rulebook, but the interpretations are endless, and ultimately lie with you as the GM at a mechanical standpoint, and with your players in how they define their characters’ morality.

It sounds like your player is trying to achieve a temporary alignment shift, with this logic: If their evil character does some good deeds, then their alignment will shift to good, and therefore they won't ping as evil for Detect Evil. After that, they can return to their evil ways, at no cost.

The following excerpts in the "Changing Alignment" section are relevant:

Aside from merely having misunderstood what a specific alignment means, PCs might seek to change their alignment in light of game events or to qualify for some alignment-related goal. How this change takes shape should be determined by the player and GM.

This means that both the player and GM should agree before an alignment change takes place. An evil creature can prompt an alignment shift by consistently doing good, but no alignment shift actually occurs if the GM disallows it. And the GM may disagree because...

Players should be sure of their decision, as changing alignment should be the result of an extraordinary effort, not a whim, and a PC with a shifting personality risks losing definition as a character and might begin to seem like he’s trying to exploit the rules.

The character is already evil, and intends to continue doing evil things in the future. The GM can decide that their attempts to score some cheap karma points are insufficient to change their character's alignment.

As GM, you should probably communicate your interpretations on alignment to your players, and explain this beforehand. It may seem unfair if they believe their character is non-evil and thus safe from the paladin, and suddenly the GM springs a "Surprise! You're evil!" on them.

Side note

Your player seems to be under a faulty premise about what Detect Evil does.

You can sense the presence of evil.

It does not detect the presence of good. If evil is in the area being analyzed, then the presence of good cannot trick the spell. Unless the good deeds were enough to shift the creature's alignment to non-evil, any good deeds are irrelevant for the purposes of this spell. The spell does what it says it does, and cannot be "fooled", unless one uses a spell or feature that explicitly says so.

Answer 2

No, they cannot

They are relying on this single line of Detect Evil for their plan:

Creatures with actively evil intents count as evil creatures for the purpose of this spell.

However, this isn't an exception, this is an addition to what should be detected by the spell. Doing good actions would probably allow them to ping inside the effect of Detect Good, but doesn't exactly prevent them from being detected as evil unless their alignment actually changes as well.

They have to change their alignment before they are able to fool Detect Evil. Either that or use other means of fooling the spell (which I suppose you are well aware of). But merely doing good actions won't have a change on their alignment, unless those actions were enough to warrant an alignment shift, which is entirely is your decision as GM.

The game doesn't leave you helpless there, though, it actually has some guidelines, which are optional rules from Champions of Purity, that details (with rules) how to convert an evil creature towards good, and says:

Simply committing a series of good acts is not enough to change a creature’s alignment—it must want deep down within itself to be good.

I won't quote all the text, only the relevant mechanical value of it, but here are the important bits about trying to move away from evil according to the book:

Penances: To pass through each stage of its path to good, a creature must perform a number of good deeds equal to double its total Hit Dice. The GM decides exactly which penances are appropriate, but examples of such acts are included below.

When a creature completes the penances required for a stage, it must succeed at a Will save to overcome its nature. The DC of this save is equal to 10 + 1/2 the creature’s total Hit Dice + its Charisma modifier. If this save is successful, the penances have taken hold and the creature has completed another step toward becoming good. If the creature fails this save, it must complete another deed in order to gain a chance to attempt another save. It can continue to complete additional deeds after each failed save until it succeeds.

And here is a small list of deeds that count as a single penance for their quest to goodness:

• Confessing your past sins or evil acts to an appropriate good-aligned agent.
• Healing a creature you don’t know from a disease, affliction, or poison when doing so gives you no personal advantage.
• Willingly submitting to a geas/quest, mark of justice, or similar spell to show you are committed enough to the process of redemption to risk harm if you fail.
• Casting a spell with the good descriptor. This penance can be completed only once per stage.
• Donating at least 50 gp to a good organization or faith. Each time you do so, the amount needed for the donation to qualify as a penance doubles.
• Sacrificing belongings gained through evil means.
• Freeing an oppressed, enslaved, or abused creature.
• Preaching a sermon of no less than 1 hour on the virtues of good behavior. This penance can only be completed once per week.
• Turning a creature that has committed a crime over to a good-aligned authority.
• Completing a task or quest for a good faith or organization without accepting payment. A GM may decide that a particularly challenging encounter may count as two or more penances.
• Fasting and praying for 12 hours (leading to fatigue).
• Creating a good item and giving it away for free.
• Showing mercy to a vanquished foe.
• Completing a task for a stranger and accepting no reward.
• Refraining from blasphemy or bad language in private or in conversation with others.
• Instructing other characters or NPCs in pure courses of action.
• Ignoring or not responding to insults or challenges from foes.
• Attempting a Diplomacy check to try and resolve a situation peaceably instead of resorting to combat.
• Refraining from lying or deception for an entire week.

A special note is required here: Casting [Good] spells can shift your alignment. Just like casting evil spells can change your alignment to evil, you could cast spells with the [good] descriptor and shift your alignment to neutral (and then good). But this can only be done once per stage (evil -> neutral then neutral -> good), meaning that multiple casts of Protection From Evil isn't enough to shift you away from evil.

If they are 5th level, that means they will need at least 10 penances before they are allowed their Will check (against a DC of 12 + their charisma bonus) to change their alignment. A first level character would need to do two penances before they are allowed a Will check, and failing it would require another penance before they are allowed to try again.

But any evil acts during that process will count against their goal (see Relapses).

Answer 3

"Men hold in their hearts both good and evil."

Pardon my Saxon.

So, Pathfinder's version of detect evil has an interesting rider on it:

Creatures with actively evil intents count as evil creatures for the purpose of this spell.

And of course, detect good (and law, and chaos) are just noted down as detect evil but with some find-and-replace on the alignments.

So, yes, acting with a good intent will make you detect as good. But if you're evil-aligned and sufficiently leveled that it gives you "an evil aura", you'll also detect as evil. And I don't believe Paladins actually have canonical access to detect good, so there's really no way to take any kind of advantage of that unless the paladin has a trusted cleric buddy or something.