 \(P\) is an essential property of an object \(o\) just in case \(o\) has \(P\) and it is necessary that \(o\) has \(P\) if \(o\) exists, whereas \(P\) is an accidental property of an object \(o\) just in case \(o\) has \(P\) but it is possible that \(o\) lacks \(P\) and yet exists. 