
The four Houses were rather separate entities. However, as a child, Snape's sadism, disdain for Muggles, and sheer cunning and ambition may have led to his being sorted into Slytherin when he first came to Hogwarts. At one point, Albus Dumbledore observed that his loyal, courageous nature was much more befitted to Gryffindor. One of the biggest examples of this was Severus Snape. A true Slytherin would not have had any doubts about whether or not it was the right House for them. He was clever, resourceful and cunning, yet the Sorting Hat made him a Gryffindor because the very fact that he asked not to be in Slytherin showed that he did not belong there. Harry Potter, for instance, embodied many of the traits that were approved and appreciated by Salazar Slytherin. Just because someone was placed in a certain House did not mean that they could not display characteristics of other Houses. The Hat also appeared to take the students' wishes into account, considering how one's personal choices are very much of a reflection of the qualities that they valued in themselves. However, these qualities did not fully surface until Neville learned to believe in himself. Case in point, Neville Longbottom was sorted into Gryffindor because the Hat sensed that he was capable of demonstrating bravery and leadership during his time at Hogwarts. The Sorting Hat could detect nascent qualities in a student and place them in the House that would challenge them and put their character to the test. Hermione Granger, while more than clever enough for Ravenclaw, valued courage above all, and was sorted into Gryffindor, a House she said sounded "by far the best". They flocked around Draco Malfoy, who they admired and who exhibited the traits of Slytherin. Other examples include Vincent Crabbe and Gregory Goyle, who despite being stupid and rather lazy, were placed in Slytherin, the House of the cunning and ambitious. He may have been placed there because, at the time, he admired strong, brave individuals like James Potter and Sirius Black. One example of the former is Peter Pettigrew, who was sorted into Gryffindor but ultimately turned out to be quite cowardly, self-serving and corruptible. It is unclear if the Sorting Hat tended to place students based on qualities they valued or rather qualities they exhibited. " It is our choices, Harry, that show us who we truly are, far more than our abilities." - Albus Dumbledore The students said that it picked up tips from Dumbledore's office. Every so often it would sing of mortal peril at the school. Before beginning the Sorting Ceremony, it sang a short song about the founding of the school and the four Houses the Sorting Hat's songs were different every year, and the Hat was said to take all year composing the next one (according to Ronald Weasley). The Sorting Hat announced the House the student was to join. At the beginning of each school year, the magical Sorting Hat was placed on each new student's head during the Sorting Ceremony. When the founders worried how students would be selected after their deaths, Godric Gryffindor took his hat off and each "put some brains" in it, creating the Sorting Hat to choose future students for each House.

In the early days of Hogwarts, the four founders handpicked students for their Houses. These two competitions bred rivalries between the Houses, the greatest of which was that between Gryffindor and Slytherin. Each House also had its own Quidditch team that competed for the Inter-House Quidditch Cup. The House with the most points won the House Cup. The houses competed throughout the school year, by earning and losing points for behaviour.

Each year's group of students in the same House shared the same dormitory and many classes. Houses at Hogwarts were both the living and learning communities for its students.
