In explaining to Romeo that names – in their case, Capulet and Montague – are mere signifiers that have no meaning, Shakespeare's Juliet raises a question that had been in constant discussion since Antiquity as part of the philosophical debate on the question of universals – were names mere signifiers, or did they carry some essence of the bearer? The problem of universals was first codified in a set of questions by Plato, found in many of his dialogues including Parmenides, and the medieval debate on universals was essentially a continuation of the ancient discussion. As established in Chapter 1, some thirteenth-century theologians tentatively attempted to divide magic into two camps: one which obtained its powers from demons, and was a forbidden perversion of Christianity; and another which operated via the hidden virtues of nature, and was a branch of natural philosophy. The argument put forward by scholastics such as William of Auvergne and the anonymous author of the Speculum astronomiae was that natural magic was a part of God's creation and therefore permissible.

In order to think about where onomancy might sit in this new way of thinking about magic and divination, we must now take a deeper dive into the main operative elements of onomantic devices – names and numbers. Were numbers the basic unit of nature, as per Platonic realism? Were names more than arbitrary signifiers? However, names and numbers were not the only Platonic associations of onomantic devices in the Middle Ages. Many onomancies were more than simply texts – they had a visual element, most obviously in the case of the ‘Sphere’. The accretive attraction between the often round figures of onomancy and Platonic representations of the round universe that pervaded medieval visual culture, as well as a plethora of other round figures in manuscripts and circular forms in art and architecture, could give onomancy a veneer of acceptability in a multitude of ways but also associate it with demonic magic. The analysis of these philosophical and visual associations of onomancy will demonstrate the way in which this form of divination might occupy a liminal space between the forbidden demonic and the permissible natural in the eyes of those who copied, read and practised it.