Thought

• Type: Magical Substance, Memory
• Owners: The witch or wizard from whom the thought originates. Can be given to or stored by others, such as Albus Dumbledore or Severus Snape.
• Maker: The mind of a witch or wizard.

A thought, when magically extracted from the mind, appears as a silvery, wispy, and ethereal substance. It is described as being neither liquid nor gas, often resembling strands of light or threads of silvery-white material that float and swirl. When extracted using a Wand placed to the temple, it is drawn out in a continuous, shimmering strand. Thoughts can be collected and stored in magically protected containers like crystal vials, where they continue to swirl and gleam. When poured into the stone basin of a Pensieve, a thought merges with the existing contents, causing the surface to ripple like water before becoming clear to reveal the scene of the memory.

The primary magical property of a thought is that it is a physical manifestation of a memory. This allows a witch or wizard to remove a memory from their mind for external storage, review, or simply to unburden their consciousness.

• Viewing Memories: The most common use of a collected thought is to view it within a Pensieve. This unique process allows the viewer to immerse themselves in the memory, experiencing it from a third-person, omniscient perspective. This vantage point allows for the observation of details that the original owner of the memory may have missed or forgotten.
• Storage: Thoughts can be stored indefinitely in containers like vials, perfectly preserving the integrity of the memory. Albus Dumbledore was known to keep a large, shelved collection of thoughts from various individuals to aid his research and planning.
• Mental Relief: Albus Dumbledore explained to Harry Potter that he sometimes used the Pensieve to siphon off excess thoughts and memories when his mind felt cluttered, allowing for clearer and more focused thinking.
• Concealment: Thoughts can be deliberately removed and stored to hide them from a Legilimens. Severus Snape meticulously removed specific memories related to his past and his allegiance to Dumbledore before his Occlumency lessons with Harry to prevent him from accidentally viewing them.
• Modification: It is possible to magically tamper with thoughts and memories. Horace Slughorn altered his memory of a conversation with a young Tom Riddle about Horcruxes. The modified thought he provided to Dumbledore was thick with white fog at the crucial moment, obscuring the truth out of Slughorn's deep shame and fear.

The practice of extracting thoughts is ancient and intrinsically linked to the creation and use of the Pensieve. The Pensieve found in the Headmaster's office at Hogwarts is of ancient origin, implying that the magic to manipulate thoughts has existed for many centuries. Throughout the series, the collection and review of thoughts are practiced primarily by powerful and skilled wizards like Albus Dumbledore. He amassed a vast collection of memories—both his own and those he persuaded others to give him—to piece together the history of Lord Voldemort. Severus Snape also regularly employed the practice, not only to hide his own thoughts but also, in his final moments, to give Harry Potter a cascade of his most crucial memories. This final act of giving his thoughts was essential to the war effort.

Extracted thoughts serve as a critical narrative device, particularly in Harry Potter and the Half-Blood Prince and Harry Potter and the Deathly Hallows. In the sixth book, Harry's private lessons with Albus Dumbledore consist almost entirely of viewing a curated series of collected thoughts in the Pensieve. These memories reveal Lord Voldemort's history, from his maternal lineage in the Gaunt Family to his creation of the first Horcruxes. The central plot of the book revolves around Harry's mission to retrieve the complete, untampered memory from Horace Slughorn. In the final book, a dying Severus Snape gives Harry Potter a silvery collection of his thoughts. When viewed in the Pensieve, these memories provide the series' most profound revelations: Snape's lifelong love for Lily Evans, his true allegiance as a double agent for Dumbledore, the complete story behind Dumbledore's death, and the monumental fact that Harry himself is an unintentional Horcrux who must willingly sacrifice himself to ensure Voldemort's defeat.

• In the film adaptations, thoughts are consistently visualized as a silvery, liquid-like substance that is drawn from a person's temple using the tip of a Wand and can be caught in a Vial. (film)
• On the Wizarding World website, J.K. Rowling expanded on the magic of the Pensieve, explaining that it shows the reality of a memory, free from the bias or interpretation of its owner. This is why a memory must be magically tampered with, as Horace Slughorn did, to be factually altered. (Pottermore)