Invocation's theoretical roots reach back to late antique Neoplatonic theurgy, the practice, associated above all with the philosopher Iamblichus, of ritual acts intended to unite the practitioner with divine principles rather than merely to contemplate them intellectually, a departure from earlier Platonism that drew criticism from more purely philosophical Neoplatonists even at the time. That theurgic model, largely lost to Western practice for centuries, was reconstructed and adapted by nineteenth century ceremonial magicians, the Golden Dawn prominent among them, who built invocation into a structured technique for assuming a deity's qualities within a magical working, typically through a mix of visualization, vibrated divine names, and ritual gesture rather than the specific theurgic operations of antiquity.
How literally to take the union described is a live difference across the traditions that use the term: some traditions describe invocation as producing genuine possession, the invoking party's ordinary consciousness set aside while the invoked force acts through them, most explicitly in traditions such as certain African diasporic religions, while Western ceremonial magic more often frames it as a deliberate, retained assumption of qualities the magician continues to direct, closer to disciplined role adoption than to displacement. Both are called invocation, and the difference in how much control the practitioner is understood to retain is substantial rather than a matter of emphasis.