In this study, we explicate citing behavior in the writing of scientific papers by presenting a taxonomy of motives to cite. The suggested taxonomy consists of four main categories, which are purely descriptive: Argumentation, Social Alignment, Mercantile Alignment, and Data. These categories are divided into a suggested set of subcategories. We argue that the complexities of citing practice show how little can be assumed about actual citing behavior when studying a finished paper. The discussion supports the claim that it might be misleading to treat all citations as equal in quantitative citation analysis.