Difference and sameness -- or identity -- are correlated concepts: to understand one is to understand the other. I will distinguish two accounts of sameness and difference: first, an essentialist account of sameness against which an understanding of difference is presented as derivative; secondly, a contextualist account which relates both sameness and difference to a more fundamental horizon or context. I will contrast two kinds of horizons, synchronic and diachronic, and within diachronic contexts I will discuss the biological horizon and the cultural or moral horizon.