Arithmancy

Arithmancy is a branch of magic that involves the study of the magical properties of numbers and is used as a form of divination. Unlike the often imprecise art of Divination as taught by Sybill Trelawney, Arithmancy is portrayed as a highly logical and precise discipline requiring mathematical calculations and complex charts to predict the future. It is considered a rigorous and intellectually demanding subject at Hogwarts School of Witchcraft and Wizardry.

Arithmancy is offered as an elective subject at Hogwarts, available for students to choose at the end of their second year to begin studying in their third. It is known to be one of the more difficult electives.

• Professor: Septima Vector (name sourced from J.K. Rowling's website).
• Classroom: Classroom 7A, located on the seventh floor of Hogwarts Castle. (Pottermore)
• Required Materials: Students require parchment, ink, a quill, and textbooks. Complex numerical charts are a key component of the homework.
• Known Students: Hermione Granger is the most prominent student of the subject in her year. Harry Potter and Ron Weasley opted not to take Arithmancy, choosing Divination and Care of Magical Creatures instead.

Hermione Granger considered Arithmancy to be her favorite subject, finding comfort in its logical framework. She often had to complete complicated homework for the class, including writing essays and interpreting charts, which she seemed to enjoy far more than the vague predictions required for Divination.

• Hermione Granger: The most notable practitioner among Harry Potter's contemporaries, she excelled at the subject and earned an 'Exceeds Expectations' on her O.W.L. exam.
• Professor Vector: The witch who taught Arithmancy at Hogwarts during the 1990s.
• Bridget Wenlock: A famous 13th-century Arithmancer who was the first to establish the magical properties of the number seven. (Famous Wizard Card)

Arithmancy primarily serves as a character-defining element for Hermione Granger, highlighting her intellectual prowess, logical mind, and academic diligence in contrast to Harry Potter's and Ron Weasley's more practical or instinct-driven approaches. The principles of Arithmancy become directly relevant to the plot in Harry Potter and the Deathly Hallows. While trying to understand the significance of Lord Voldemort creating seven Horcruxes, Hermione applies her knowledge of the subject. She states, “…and seven's the most powerfully magical number, it'd be a suitable number of fragments for a soul to be split into.” This insight provides a logical, magical framework for Voldemort's actions and underscores the deep-seated power associated with the number seven in the wizarding world.

The name “Arithmancy” is derived from two Greek words:

• arithmos (ἀριθμός), meaning “number.”
• manteia (μαντεία), meaning “divination” or “prophecy.”

The combination directly translates to “divination by numbers.”

• The name of the Arithmancy professor, Septima Vector, was revealed by J.K. Rowling on her original website and was not mentioned in the novels. Her first name, Septima, is Latin for “seventh,” alluding to the magical properties of the number seven discovered by Bridget Wenlock. Her surname, Vector, is a term from mathematics and physics, fitting for a teacher of a number-based discipline.
• In the film adaptations, Arithmancy is mentioned as a subject Hermione Granger takes but is never shown, and its role in deciphering the significance of seven Horcruxes is largely omitted.