In recent years there has been a growing research interest in the field of animal emotion. But there is still little agreement about whether and how the word "emotion" should be defined for use in the context of non-human species. Here, we make a distinction between descriptive and prescriptive definitions. Descriptive definitions delineate the ways in which the word emotion is used in everyday life. Prescriptive definitions are used to pick out the set of events that scientific theories of emotion purport to explain. Picking out three prescriptive definitions, we show that the different ways in which emotions are defined correspond to processes that are distributed differentially across the animal kingdom. We propose that these definitions provide a useful starting point for investigating the varying emotional capacities of a wide range of animals, providing a basis for a new, comparative science of emotion.
Keywords: Affect; Animal behaviour; Animal emotion; Consciousness; Definition; Emotion.