A father hands his young son a half of a sandwich for lunch. The boy begins to cry, "I want two!" When his mother quickly cuts his sandwich in two he begins happily eating his lunch. The father says, with concern in his voice, "Is there something wrong with him?" The boy's mom, who just finished a psychology course explains, "No honey, he just can't understand ___________ yet; he's in the ____________ stage of cognitive development."
