Earl is one of the ranks assigned to the spirits catalogued in the grimoire tradition, and above all in the Ars Goetia, the first book of the seventeenth-century Lesser Key of Solomon (Lemegeton). It denotes a rank sometimes given with the alternative title Count, standing among the middle nobility of the hierarchy.
The ranks of the spirits
The Goetia lists seventy-two spirits and gives most of them a rank, King, Prince, Duke, Marquis, Earl or Count, President, or Knight, borrowed from the feudal and civil offices of the human world, together with the number of legions each is said to command. The scheme draws on earlier sources, notably the Pseudomonarchia Daemonum printed by Johann Weyer in 1577.
The rank is described here as a feature of these documented magical texts, studied as historical literature; the spirits so ranked are not reified.
Earl is the odd one out among the Goetia's titles in a specific linguistic way: it descends from Old English and Old Norse eorl, a native Anglo-Saxon and Scandinavian rank of nobility, where every other title in the catalogue, Duke, Marquis, Prince, comes into English through French. After the Norman Conquest, the incoming French nobility used comte, "count," for the equivalent continental rank, and English retained earl for the man while nonetheless adopting the French-derived countess for his wife, since no native feminine form existed, a mismatch that survives in English today and explains why the catalogue itself gives the rank as "Earl, or Count.
Sources Lemegeton Clavicula Salomonis (The Lesser Key of Solomon)Anonymous (unidentified compiler) with Encyclopaedia Britannica (online academic reference)Encyclopaedia Britannica editors