Inadvertence is when you do something without realizing what you are doing — a slip that comes from not noticing, not from a plan. A letter goes to the wrong person through inadvertence. You knock a glass by inadvertence. It is a noun, and a rather old, formal one. Lawyers and careful writers still like it. In everyday talk, people more often say “by accident” or “I didn’t realize”. Though actually it is not the same as not caring. Inadvertence is a gap in attention. “On purpose” is the opposite feeling. The forms you will hear much more are inadvertent and inadvertently.

疏忽、無心（偏「沒注意到」，不是存心；書面、法律較常見）