In this paper, I put forward a benchmark account of emergence in terms of non-explainability and explicate the relationship that exists between its synchronic and diachronic declinations. I develop an argument whose conclusion is that emergence is essentially a “two-faceted” notion, i.e. it always encapsulates both synchronic and diachronic dimensions. I then compare this account with alternative recent accounts of emergence that define the concept through the notion of unpredictability or topological non-equivalence.