Vow

A Vow in the wizarding world is a magically binding promise. While various types of promises and oaths may exist, the most powerful and explicitly detailed example in the series is the Unbreakable Vow. This form of magic binds a witch or wizard to a promise under the penalty of death, making it one of the most serious and dangerous magical undertakings known. It is not a spell cast with a single incantation but a formal magical ritual.

The Unbreakable Vow is a magical contract made between two people, which is sealed and enforced by a third person known as the Bonder. It is considered exceptionally grave magic, and breaking it results in the death of the person who made the promise.

The performance of an Unbreakable Vow requires three participants and a specific procedure:

1. The two individuals making the pact, the promiser and the promisee, kneel opposite each other and join their right hands.
2. A third witch or wizard, the Bonder, stands over them and places the tip of their wand upon the participants' clasped hands.
3. The promisee asks the promiser to agree to one or more terms.
4. With each term the promiser agrees to, a thin tongue of bright flame issues from the Bonder's wand and winds itself around the participants' hands. These flames form a chain-like binding, signifying the magical seal of the vow.

The primary and most fearsome feature of the Unbreakable Vow is its absolute nature. As explained by Ron Weasley, it is a vow that cannot be broken. The magical consequence for failing to uphold the promise is death. This is not a curse inflicted by another person but an inherent part of the magic of the vow itself.

• Severus Snape's Vow to Narcissa Malfoy (1996): This is the most significant instance of an Unbreakable Vow in the series. It takes place at Snape's House in Spinner's End, with Bellatrix Lestrange acting as the Bonder. Narcissa Malfoy implores Snape to help her son, `Draco Malfoy`, who has been tasked with a secret mission by Lord Voldemort. Snape makes three promises:
  1. To watch over Draco as he attempts to fulfill the Dark Lord's wishes.
  2. To protect Draco from harm to the best of his ability.
  3. To carry out the deed that the Dark Lord has ordered Draco to perform—the murder of Albus Dumbledore—if Draco should fail.
• Fred Weasley and George Weasley's Attempted Vow with Ron Weasley: Ron mentions that his twin brothers once tried to get him to make an Unbreakable Vow. Their father, Arthur Weasley, discovered them and became the angriest Ron had ever seen him. This incident establishes that the vow is known in the wider wizarding community and is considered extremely serious and inappropriate for children to meddle with.

The Unbreakable Vow is a critical plot device, particularly in Harry Potter and the Half-Blood Prince. Snape's vow to Narcissa provides a magically inescapable reason for his actions, most notably his killing of Albus Dumbledore. This act is essential to Dumbledore's master plan to defeat Voldemort, as it solidifies Snape's position as a trusted Death Eater while simultaneously being an act of mercy for Dumbledore himself. The vow adds a profound layer of complexity and sacrifice to Snape's character, as he is magically bound to fulfill his promise, forcing his hand and cementing his role as a tragic hero.

• In the film adaptation of Harry Potter and the Half-Blood Prince, the visual effect of the Unbreakable Vow includes the tongues of flame searing a glowing, scar-like mark onto the skin of Snape and Narcissa's arms, a detail not explicitly mentioned in the novel. (film)