Hermeticism, or Hermetism, is a label used to designate a philosophical system that is primarily based on the purported teachings of Hermes Trismegistus (a legendary Hellenistic combination of the Greek god Hermes and the Egyptian god Thoth).[1] These teachings are contained in the various writings attributed to Hermes (the Hermetica), which were produced over a period spanning many centuries (c. 300 BCE – 1200 CE), and may be very different in content and scope.[2]

One of the most common uses of the label is to refer to the religio-philosophical system propounded by a specific subgroup of Hermetic writings known as the 'philosophical' Hermetica, the most famous of which is the Corpus Hermeticum (a collection of seventeen Greek Hermetic treatises written between c. 100 and c. 300 CE).[3] This specific, historical form of Hermetic philosophy is sometimes more restrictively called Hermetism,[4] to distinguish it from the philosophies inspired by the many Hermetic writings of a completely different period and nature.

A more open-ended term is Hermeticism, which may refer to a wide variety of philosophical systems drawing on Hermetic writings, or even merely on subject matter generally associated with Hermes (most notably, alchemy often went by the name of "the Hermetic art" or "the Hermetic philosophy").[5] The most famous use of the term in this broader sense is in the concept of Renaissance Hermeticism, which refers to the wide array of early modern philosophies inspired by, on the one hand, Marsilio Ficino's (1433–1499) and Lodovico Lazzarelli's (1447–1500) translation of the Corpus Hermeticum, and on the other, by Paracelsus' (1494–1541) introduction of a new medical philosophy drawing upon the 'technical' Hermetica (i.e., astrological, alchemical, and magical Hermetica, such as the Emerald Tablet).[6]

In 1964, Frances A. Yates advanced the thesis that Renaissance Hermeticism, or what she called "the Hermetic tradition", had been a crucial factor in the development of modern science.[7] While Yates's thesis has since been largely rejected,[8] the important role played by the 'Hermetic' science of alchemy in the thought of such figures as Jan Baptist van Helmont (1580–1644), Robert Boyle (1627–1691) or Isaac Newton (1642–1727) has been amply demonstrated.[9]

Throughout its history, Hermeticism was closely associated with the idea of a primeval, divine wisdom, revealed only to the most ancient of sages, such as Hermes Trismegistus.[10] In the Renaissance, this developed into the notion of a prisca theologia or "ancient theology", which asserted that there is a single, true theology which was given by God to some of the first humans, and traces of which may still be found in various ancient systems of thought. Thinkers like Giovanni Pico della Mirandola (1463–1494) supposed that this 'ancient theology' could be reconstructed by studying (what were then considered to be) the most ancient writings still in existence, such as those attributed to Hermes, but also those attributed to, e.g., Zoroaster, Orpheus, Pythagoras, Plato, the 'Chaldeans', or the Kaballah.[11] This soon evolved into the idea, first proposed by Agostino Steuco (1497–1548), that one and the same divine truth may be found in the religious and philosophical traditions of different periods and places, all considered as different manifestations of the same universal perennial philosophy.[12] In this perennialist context, the term 'Hermetic' tended to lose even more of its specificity, eventually becoming a mere byword for the purported divine knowledge of the ancient Egyptians, especially as related to alchemy and magic. Despite their occasional use of authentic Hermetic texts and concepts, this generic and pseudo-historical use of the term was greatly popularized by nineteenth- and twentieth-century occultists.[13]