Use this when you want to say that something has two aspects at once, often ones that seem to pull in different directions or that you want to weigh equally. It's like saying 'is both X and Y' in a somewhat formal, literary way. For example, you might describe a person as both a parent and a professional, or a situation as both a crisis and an opportunity. It often appears in written language, essays, speeches, or thoughtful conversation. In speech, you might hear it when someone is being reflective or making a deliberate point. The structure is built on the て-form of ある (which is あり), so the first part is Aでもあり, then the second part is Bでもある. The pattern emphasizes the coexistence of the two, rather than just listing them. Be careful not to confuse it with the simpler でもある alone, which just adds one more attribute to a single subject. Here, the double structure is key: you need both でもあり and でもある to create the sense of duality.