 The boundaries between these different types of goods are neither sharp nor fixed. For example, whether or not Bob’s enjoyment of a movie in a theatre is affected by Sally’s watching the movie in the same theatre at the same time depends on Bob’s values or tastes as well as details of the context. Sally might sit in front of Bob and partially block his view. Or she might be one of those people who sits right next to you even though fifty other seats are available. Or Bob might be bothered by anyone sitting in the same theatre at the same time, or enjoy watching the movie together with others. Thus, even supposing that Sally doesn’t alter Bob’s viewing of the movie as such, her presence can have a positive or negative effect on Bob’s enjoyment of it. Thus, whether or not a good is rivalrous in consumption depends on many contextual details and not just the nature of the good alone.