In Harry Potter, there are four Hogwarts houses into which students are placed by the Sorting Hat on their first day of school. In the epilogue of Harry Potter and the Deathly Hallows, Harry tells his middle child Albus Severus the Sorting Hat takes a kid's choice into account when making its decision on where to place them; however, this is only partly true. By piecing together clues from multiple characters, it is reasonable to deduce that Gryffindor is actually the only house a student can choose.

Exploring the characteristics of some of the series' favorite Gryffindors allows this theory to take shape.

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When Harry Potter was sorted, the Sorting Hat took his choice into account. When Harry first arrived at Hogwarts and placed the Hat upon his head, he was told that he would do well in Slytherin. He begged the hat to put him anywhere but Slytherin and the Hat obliged. Harry did not explicitly say he wanted to be in Gryffindor, but it certainly shows a lot of nerve to reject the Hat's assessment -- and Gryffindors are characterized by their bravery.

Harry's best friend Ron Weasley also could have easily been sorted into another house, but ended up in Gryffindor. Ron demonstrates some of the values of a classic Hufflepuff. He is fiercely loyal and a believer in justice. He would have done well in Hufflepuff and he might have done better not being in the same house as his entire family.

However, Ron always wanted to be a Gryffindor. He wants to be in the same house as his family and his new friend Harry Potter. While it's not explicitly stated, it's fair to assume that when Ron put the Hat on his head, he was thinking long and hard about his deep desire to be a Gryffindor. So even if he didn't directly ask the Hat to be sorted into Gryffindor, deep down the Hat could read his desperate pleas for that very outcome.

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Hermione Granger was very nearly a Hatstall. A true Hatstall is when the Sorting Hat requires more than five minutes to sort a student. The Hat seriously considered placing Hermione into Ravenclaw, which seems like the obvious house for brainy bookworm Hermione; Ravenclaws value intelligence and learning.

It's likely her tenacity and righteous fury ultimately pushed the Hat to place her in Gryffindor. It's not explicitly stated how the Hat came to its decision, but there had to be something in Hermione's subconscious, at the very least, that openly desired Gryffindor, besides her natural inclination to behave in a Gryffindor manner.

Percy Weasley is another example of someone who seems like a perfect fit for a different house but was ultimately sorted into Gryffindor. Percy is a classic Slytherin. He is extremely ambitious and demonstrates a thirst for leadership. He betrays his family in Harry Potter and the Order of the Phoenix in favor of his own career ambition. Even prior to this, Ron predicts Percy would put his career before family, during a discussion about Barty Crouch sentencing his own son to Azkaban.

If Percy is such an exemplary Slytherin, then why would the hat put him in Gryffindor? When he was 11 years old, Percy wanted to be in the same house as his parents and two older brothers. There does not seem to be any other explanation for why Percy would be in Gryffindor unless he asked for it.

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Finally, some may believe Neville Longbottom disproves this theory altogether because he so desperately begged the Hat to sort him anywhere BUT Gryffindor. Actually, this only further reinforces the point that Gryffindors choose to be there, even if that choice is not explicit.

Neville desperately wants to live up to his parents' reputations and the expectations of his overly critical Grandmother, but is afraid he can't. He wants to be a Gryffindor, but is scared he won't measure up. Neville, like Hermione, was very nearly a Hatstall. Without knowing it, Neville demonstrated the same courage and nerve Harry did while being sorted, meaning if Harry asked to be a Gryffindor, so did Neville. He sat under the hat for almost five minutes arguing, which shows a remarkable amount of bravery.

Neville also serves to prove that asking for another house does not mean a student will be sorted there. He specifically requested to be sorted into Hufflepuff and was denied that request.

The Sorting Hat investigates students' inner thoughts and deeply hidden emotions to determine what their true values are and therefore, in which house they belong. Each house has their own strengths and weaknesses, but sometimes a student will have a specific request of the Hat. While it is possible the Hat always take their choices into account, Gryffindor appears to be the only house a student can request and actually be sorted into.

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