Renaissance and early modern Europe. Ptolemaic astrology continued to be taught at European universities into the 17th century, but by the mid-17th century the study struggled to maintain its position as one of the respected Liberal sciences. At this time, the contents of the Tetrabiblos started to draw stigmatisation as part of "a diabolical art of divination". One 17th-century critic was to write of its subject: "no superstitious art is more fitted to forward the aims of the devil than the astrology of Ptolemy". The intellectual standing of astrology collapsed rapidly at the end of the 17th century, but the historical impact of the Tetrabiblos upon world culture continues to engage the attention of scholars of classical philosophy and the history of sciences in antiquity. It also maintains its position as an influential textbook for practitioners of modern western astrology, and English translations of the text were published by astrologers in the 18th, 19th and 20th centuries. The early 20th-century Humanist astrologer Dane Rudhyar reported that the astrology of his era "originated almost entirely in the work of the Alexandrian astrologer, Claudius Ptolemy". Even 21st-century astrological textbooks have described the Tetrabiblos as being "without a doubt, indispensable for any serious student of astrology". The work's enduring significance is attributed to several factors: Ptolemy's reputation as one of the greatest philosophers and scientists of the ancient world, the text's astrological importance as one of the oldest complete manuals on that subject, and the unprecedented order and quality of Ptolemy's astrological explanations. The "outstanding mark of Ptolemy’s astrology" is described as "informed by the philosophical and scientific spirit of his age". Ptolemy wrote at a time when "physics" was defined by philosophy, and his account of stellar effects was expressed in terms of the four Aristotelian qualities (hot, cold, wet, and dry) set against the philosophical notion of universal unity and cosmic harmony. His objective was to explain the rationale of astrology in such terms, so the work is also notable for its dismissal of astrological practices which lack a direct astronomical basis: The book opens with an explanation of the philosophical framework of astrology which aims to answer the arguments of critics who questioned the subject's validity. Of this, Lynn Thorndike, in his History of Magic and Experimental Science, writes: "Only the opponents of astrology appear to have remained ignorant of the Tetrabiblos, continuing to make criticisms of the art which