Philosophus is the fourth and final grade of the Societas Rosicruciana in Anglia's First Order, following Practicus. Founded in 1866 and 1867, the society is a Masonic-Rosicrucian body open only to Master Masons, and its grade names and numbering were adapted roughly two decades later by the founders of the Hermetic Order of the Golden Dawn for that order's own First Order grades, a documented lineage that runs from the SRIA to the far better known order it partly inspired.
Advancement within the SRIA's First Order, Grades I through IV, is the responsibility of the society's local Colleges, a decentralized administrative structure distinct from the Provinces that oversee the Second Order, Grades V through VII, and the Supreme Magus who alone administers the Third, Grades VIII and IX. This tiered administration, College to Province to Supreme Magus, mirrors the Golden Dawn's own later First, Second and Third Order division closely enough that the parallel is treated as more than coincidental in the scholarly history of both bodies.
Because the SRIA predates the Golden Dawn and continues to exist as its own Masonic-Rosicrucian society, Philosophus and its First Order companions are documented in Masonic reference literature as the template a far more widely studied order later drew on, rather than as a derivative of it.