How we cite our quotes: (Act.Scene.Line)
Quote #1
JAMES: I only said he might be in Slytherin. (1.1.4)
It would oversimplify the sorting process if you thought that your house defined your personality instead of the other way around. Albus is too young to realize this—as Harry once was—and he thinks that being Slytherin might make him evil. It's a self-fulfilling prophecy of sorts.
Quote #2
HARRY: Albus Severus, you were named after two headmasters of Hogwarts. One of them was a Slytherin and he was probably the bravest man I ever knew. (1.2.37)
Harry set high expectations for his son by giving him these two names. Even before Albus is given the label Slytherin, he's already marked—as Harry was with his scar—with names that give him a legacy to live up to.
Quote #3
HARRY: If it matters to you, you, the Sorting Hat will take your feelings into account. (1.2.39)
Is it possible that the Sorting Hat knew that Albus not only belonged in Slytherin, but wanted to be there as a subconscious way of subverting his father's expectations? It's a play, not a novel, so we can't hear Albus' thoughts. We wouldn't be shocked to learn if he thought, I'll really stick it to dad if I get sorted into Slytherin?