  Two very different responses are available to Berkeley on this issue, each of which he seems to have made at a different point in his philosophical development. One response would be to reject spiritual substance just as he rejected material substance.  Spirits, then, might be understood in a Humean way, as bundles of ideas and volitions. Fascinatingly, something like this view is considered by Berkeley in his early philosophical notebooks (see PC 577ff). Why he abandons it is an interesting and difficult  question;[25]  it seems that one worry he has is how the understanding and the will are to be integrated and rendered one thing. 