True name

No matter the rank of a devil, knowing its true name could grant great power over it (or a horrible death).

A true name is a unique, hidden magic word that represents a person, place, or thing and is independent of any private or public names by which that thing is known.

Learning true names

Each mortal soul is inscribed with their true name, which almost never changes unless the mortal undergoes such a thorough transformation that they effectively become a new person.

It is very difficult to learn any mortal's true name; most who live in cultures lacking knowledge of the existence of true names never learn of the existence of true names, much less discover their own. However, some mortals have soulmates who instinctively know the true name of another mortal, even if they have no understanding of the concept.

There are several ways in which to learn an entity's true name, most of which require intensive research:

• Locate a "namer" in a secret society responsible for teaching others true names that have already been identified and passed down through memorization
• Find them in spellbooks or journals of spellcasters
• Locate organizations dedicated to fighting or defending against a specific opponent
• Perform meditative or hallucinogenic trances, typically by occultists
• Understand the nature of true names as recorded in the patterns and natural structures of primal entities and the First World
• Through a creature's true name amulet, which reveals its true name only to its invested wearer

Knowledge of a true name might be cursed to protect its spread or punish those who attempt to learn it.

Variations of true names

The nature of true names varies between types of creatures. For example:

• A devil's true name is mutable as it grows in stature.
• An elemental suffers no penalties when its true name is used during a binding ritual, though it often starts with a more positive attitude toward a binder who knows its true name.
• Proteans and qlippoths lack true names as they are fundamentally too chaotic.
• Aeons are rumored to have two true names, and prospective binders require both to take control of such creatures.
• Unicorns keep their true names deeply secret.

Using true names

Knowledge of an entity's true name grants one influence over and a deeper understanding of the entity, makes the entity easier to identify through its writing or magic, and improves one's ability to impersonate the entity.

In magic

Several abilities use the threat of revealing an entity's true name to compel it to act in a certain way, and related magical spells require knowledge of at least part of an entity's true name to be effective (see Fragmentary names).

Conversely, knowledge of one's own true name can allow an entity to cast a spell to learn when its private or true names are used, and by whom.

In oaths and contracts

Phistophilus devils require mortals to willingly sign their true names to infernal contracts.

A living monolith inscribes their true name and oaths into their ka stone before embedding it into their forehead.

In magic items

Making public the true name of a forgotten signet's wearer destroys it.

Destroying true names

In exceedingly rare situations, an entity's true name might be destroyed. Doing so removes all knowledge and memories of that entity's existence from reality, including from themselves if still alive when the severance occurs.

Nameless thing

When a creature, such as an aberration, celestial, fiend, monitor, or spirit, enters the Universe from another plane or another reality altogether—one where the laws of magic are different—they might not have any true name. Such creatures are designated as nameless things.

Fragmentary names

Certain spells or items that require true names can be used even when a person knows only fragments of a subject's true name, though the likelihood and dangers of failure when using a fragmentary name increase significantly.

Certain abilities related to true names, such as the compel true name spell, can also reveal fragments of the spellcaster's true name to the subject when used.

On Golarion

Kaseshi bear words of power similar to true names that reflect and empower their identities. However, "kasesh" itself is not their kind's true name, which might be known only to their creators, the Vault Builders.

Golomas of the Mwangi Expanse keep knowledge of their true names closely held secrets among their own kind, and adopt public names from Aklo, Necril, or other intimidating languages for the rare instances where they interact with other ancestries.

Cultists of the Sandpoint Devil believe that upon its consumption of 66 souls, a deity will emerge from the Pit and reveal its true name.

References

Paizo published a chapter about true names in Secrets of Magic 244ff.

For additional as-yet unincorporated sources about this subject, see the Meta page.