Discerning good from evil spirits
Here are four criteria for distinguishing divine from demonic spirits from Ludwig Lavater's demonology. I have altered the color of the third to draw attention to this test. In light of the strong Elizabethan reaction of the Anglican church against revenge, and the New Testament's unequivical position on vengeance, the spirit would have been judged evil by Shakespeare's original audience using this test.
By what tokens good spirits may be discerned from euill.
Moreouer popishe writers teache vs to
discerne good spiritis from euill by foure meanes. First thay say that
if he be a good spirit, he will at the beginning, somewhat terrifie
men, but againe soone reuiue and comfort them. So Gabriel with comfortable
words did lifte vp the blessed virgin which before was sore troubled
by his salutation. They also alleage other examples. Their second note
is to discry them by their outward and visivle shape. For if they appeare
vnder the forme of a Llyon, beare, dog, tode, serpent, catte, or blacke
ghoste, it may easly be gathered that it is an euill spirit. And that
on the othr side good spirits do appeare vnder the shape of a doue,
a man, a lambe, or in the brightnesse, and clere light of the sunne.