 There is a connotation of the word ‘substance’, reflected in the sense of substantial, which signifies durability or even permanence. Events, or Hume’s impressions and ideas are never substantial in this sense, because they are fleeting. Atoms, fundamental kinds of stuff, gods, or abstract entities, such as Platonic Forms or numbers, might be considered to be substantial to the point of being indestructible or eternal: they last at least as long as the world exists—and, in the case of gods or God, or abstract entities, perhaps longer.