 Relata of combinative preferences are not specified enough to be mutually exclusive. To say that one prefers having a dog over having a cat neglects the possibility that one may have both at the same time. Depending on how one interprets it, this preference expression may say very different things. It may mean that one prefers a dog (and no cat) to a cat (and no dog). Or, if one already has a cat, it may mean that one prefers a dog and a cat to just having a cat. Or, if one already has a dog, it may mean that one prefers just a dog to both a cat and a dog. Combinative preferences are usually taken to have states of affairs as their relata. These are represented by sentences in sentential logic. It is usually assumed that logically equivalent expressions can be substituted for each other.