[80:1] He (Al-Birūnī) quotes with approval the following, as the teaching of the adherents of Aryabhatta: It is enough for us to know that which is lighted up by the sun's rays. Whatever lies beyond, though it should be of immeasurable extent, we cannot make use of; for what the sunbeam does not reach, the senses do not perceive, and what the senses do not perceive we cannot know. From this we gather what Al-Birūnī's Philosophy was: only sense-perceptions, knit together by a logical intelligence, yield sure knowledge. (Boer's Philosophy in Islām, p. 146). [80:2] "Moreover truth for him (Ibn Haiṯẖam) was only that which was presented as material for the faculties of sense-perception, and which received it from the understanding, being thus the logically elaborated perception". (Boer's Philosophy in Islām, p. 150). [80:2] "Moreover truth for him (Ibn Haiṯẖam) was only that which was presented as material for the faculties of sense-perception, and which received it from the understanding, being thus the logically elaborated perception". (Boer's Philosophy in Islām, p. 150). CHAP. IV. CONTROVERSY BETWEEN IDEALISM AND REALISM. The As̱ẖ‘arite denial of Aristotle's Prima Materia, and their views concerning the nature of space, time and causation, awakened that irrepressible spirit of controversy which, for centuries, divided the camp of Muhammedan thinkers, and eventually exhausted its vigor in the merely verbal subtleties of schools. The publication of Najm al-Dīn Al-Kātibī's (a follower of Aristotle whose disciples were called Philosophers as distinguished from scholastic theologians) Ḥikmat al-‘Ain--"Philosophy of Essence", greatly intensified the intellectual conflict, and invoked keen criticism from a host of As̱ẖ‘arite as well as other idealist thinkers. I shall consider in order the principal points on which the two schools differed from each other. A. _The Nature of the Essence._