The term “occult” (from Latin occultus; “hidden”) has a long history in Western natural philosophy (for an overview, see Hanegraaff, 2005). In the medieval scholastic interpretation of Aristotle, the term “occult qualities” (“qualitates occultae”) was used to describe the hidden qualities of material things, related to their “form” rather than their “substance”, which could not be perceived directly but which nevertheless accounted for certain physical, observable effects. Thus, all physical properties that did not have a clearly discernible cause from the outside could be labeled occult: the property of attracting or repelling other objects was one such occult quality, but the curative or poisonous effects of herbs, mineral tonics, and “magical” amulets were also included in the same natural–philosophical category. This was, in fact, the main meaning of the word “occult” throughout the middle ages, and we find it used in this form among scholastic philosophers such as Thomas Aquinas.
Occult qualities remained an influential concept in renaissance natural philosophy. In extension, it became central for major representatives of Western esoteric thought. Occult qualities were at the foundations of “natural magic” (magia naturalis), and central to the so-called “occult sciences”, particularly alchemy. Thus, Heinrich Cornelius Agrippa von Nettesheim’s influential ‘De occulta philosophia’ (1533) described a system of three worlds with three adjoining forms of magic: the terrestrial or sub-lunar world; the astral or supra-lunar world; and the spiritual and divine world beyond the fixed stars. Natural magic belonged to the lower sub-lunar world, and it worked by the skilled use of knowledge about the occult properties of things: metals, herbs, colours, and the occult correspondences between these and the entities of higher worlds, such as the planets.
Occult properties were by no means separated from the legitimate science (or natural philosophy) of the early modern period; there was a continuum between natural magic and natural philosophy. This started to change during the scientific revolution, but not, as has often been contended, by an outright rejection of “occult properties” (cf. Hanegraaff, 2012: 177–91). It is more correct to say that the emerging mathematical and mechanical paradigm in natural philosophy, associated with names such as Galileo Galilei, René Descartes and Isaac Newton, found in mathematics a way to make the unobservable causes of “occult qualities” subject to precise measurement, explanation and prediction — a possibility that had effectively been denied by scholastic philosophy. An example of these changing tides is found in René Descartes’ ‘Principia philosophiae’ (1644): here we find a number of diagrams thought to explain the hidden mechanisms that govern previously “occult” effects such as magnetism, now made explicable by an atomic theory of matter and the principles of mechanical motion.
An effect of the rise of the so-called mechanical philosophy, which by the eighteenth-century had come to include mathematics, astronomy, physics and chemistry (with attempts to subsume biology, mental, moral and political philosophy as well, in the works of e.g. Julien Offray de La Mettrie and Thomas Hobbes) was that research paradigms that had rested on the notion of occult qualities became increasingly marginalized. One example of this process was the separation of chemistry from alchemy by the end of the seventeenth-century. This happened in the wake of Robert Boyle’s work, sometimes labelled the “father of chemistry”, who is perhaps better described as a laboratory alchemist who embraced the mechanical philosophy and achieved explanatory success thereby (cf. Principe, 1998). What followed during the eighteenth-century Enlightenment was a grand-scale rejection of entire fields of superseded knowledge in natural philosophy, most notably of alchemy and astrology. This is the context in which notions of “occult sciences” first started to take shape: alchemy, astrology and (natural) magic were all thought to share a foundation in occult qualities and correspondences, which had no place in Enlightenment epistemology.
It is thus from the Enlightenment period onwards that we can truly speak of a notion of strict separation between science and the occult — a primarily polemical dichotomy created by the process of differentiation between modern science and other domains of thought, including philosophy and theology. This process continued in the nineteenth-century, with the professionalization of the natural sciences, and the sociological differentiation of “scientists” as a separate social class, the term “scientist” having been coined by philosopher William Whewell as late as 1840.
In light of these very significant intellectual and social developments, notions of “the occult” and of science were rapidly changing and would come to take on quite different meanings. Two new developments must be mentioned here. First, the ascendency of the mechanistic philosophy led to a proliferation of pseudo-mechanical occult forces, typically formulated by people standing on the boundaries of the emerging modern sciences. Second, the Enlightenment project led to a view of the occult as pseudo-scientific and pseudo-religious “rejected knowledge”; that is, as an undercurrent of ideas that were not “scientific” because unacceptable from the standpoint of Enlightenment epistemology, and not “religious” because unacceptable from the standpoint of established church doctrine (cf. Hanegraaff, 2012).
The notion of occult forces appears to have been invented during the Enlightenment under the influence of the mechanical philosophy. Occult forces were distinct from occult qualities in that they were conceived of in terms of pseudo-mechanistic “laws”, invisible “fluids”, or “fields”, modelled on the concepts proposed in the new physics. Indeed, where the prototypical examples of occult qualities were found in the Aristotelian doctrine of forms, the prototypical occult (i.e. hidden) force was found in Newtonian gravity. The notion of material bodies pulling each other from a distance, without any observable intermediary substance, triggered the imaginations of thinkers in other fields and seemed to lend some legitimacy to postulating similar universal “laws” and invisible “forces” in other domains. In fact, a vast number of such forces, often connected to the notion of a subtle, invisible “ether”, were proposed by natural philosophers of the Enlightenment period (Asprem, 2011, 134–35). Most of these theories never made it to the status of scientific orthodoxy: Benjamin Franklin formulated an “elastic ether” theory to account for electricity, for example, while Georges-Louis Le Sage’s “kinematic ether” was offered an explanation for a wide range of phenomena, including gravity, weight, and chemical affinity (cf. Laudan, 1981).
While most of these unsuccessful theories were simply forgotten, some of that which never became an official science (at least not for any substantial period) would become highly influential in the emerging world of the post-Enlightenment “occult”. A primary example of this is Franz Friedrich Anton Mesmer’s notion of “animal magnetism”, first conceptualized as a pseudo-mechanistic theory of subtle fluids, interpenetrating the cosmos and living beings, accounting for various physical and psychical ailments as well as special mental rapports between human beings (see the article on Mesmerism and Animal Magnetism). The different theories and practices associated with Mesmerism came to exert an enormous influence on nineteenth-century esoteric currents, notably occultism and spiritualism. It provided a science-like explanation of magic in Joseph Ennemoser’s ‘Geschichte der Magie’ (1844), which in turn became the single most important influence on Helena Petrovna Blavatsky’s published works of Theosophy. Éliphas Lévi Zahed’s massively influential ‘Dogme et rituel de la haute magie’ similarly looked to Mesmerism for its account of the magical agent, “astral light”. Finally, the new interpretation of alchemy as spiritual alchemy, first outlined in Mary Anne Atwood’s ‘Suggestive Inquiry into the Hermetic Mystery’ (1850), used Mesmerism as the prism through which this physico-spiritual discipline was to be understood.
A number of other occult forces were proposed throughout the nineteenth-century, modelled on concepts taken from physics. Among these we should mention the “odic force” of the baron and industrialist Carl Ludwig von Reichenbach, a form of vital energy named after the Norse god Odin, and the “vril force”, invented by the British author Edward George Earle Lytton Bulwer-Lytton for his fantastical novel ‘The Coming Race’ (cf. Strube, 2013). All these occult forces — animal magnetism, astral light, the odic force, vril — found their way into the synthetic doctrines of the Theosophical Society, and became central “science” terms in occultism in the nineteenth- and twentieth-centuries. As forms of rejected scientific knowledge, they became important resources for occultists to challenge established science, typically perceived as “materialistic” and “dogmatic”, while at the same time claiming a form of rational knowledge for themselves (cf. Hammer, 2001; Asprem, 2012, 446–59).