The Tree of Life is an arrangement of symbols reminiscent of Platonic idealism, in which the world of sensory phenomena is held to be a secondary or degenerate form of a spiritual reality made up of pure ideas existing behind the appearance of the material world. The ideals are like lights and the events perceptible to the senses are only the shadows they cast. Centuries after the fall of Rome, first Jewish Qabala and then Christian Qabala and Renaissance magic revived the Neo-Platonic cosmological and magical tradition. It had survived for a millenium in classical works, and in the Islamic preservation of Hellenistic knowledge in Spain and Southern France. The magical revivalists developed many different symbolic representations of the idealistic universe, including the Tree of Life, the Tarot, other philosophical card decks, and alchemical and zodiacal diagrams.
Philosophy often deals with two opposing perspectives, the nominalist and the idealist.
Loosely speaking, nominalists focus on the names of things and their outward appearances as the currency of human knowledge, while idealism considers things in the world of senses to be only pale reflections of their ideal forms, or essences, or pure ideas. This plane of ideal forms is derided by nominalists but it was the basis of Renaissance philosophy and the Tree of Life. Nominalism has been crucial to existentialism and phenomenology, important parts of 20th century philosophy, while mystical idealism is not widely considered a viable philosophy today. Crowley insisted that he was not an idealist but a nominalist, while also insisting that the Tree of Life in the form known to him from the Golden Dawn truly represented the esoteric structure of reality and could only be harmed by changing its arrangement. This is one of many contradictory statements in Crowley's approach to philosophy and whether it is an inspired paradox or a careless contradiction is a subject of controversy.