To them substance and atom are identical, and they define substance as a space-filling atom which, besides the quality of filling space, has a certain direction, force and existence forming its very essence as an actuality. In shape it is squarelike; for if it is supposed to be circular, combination of different atoms would not be possible[53:5]. There is, however, great difference of opinion among the exponents of atomism in regard to the nature of the atom. Some hold that atoms are all similar to each other; while Abu’l-Qāsim of Balḵẖ regards them as similar as well as dissimilar. When we say that two things are similar to each other, we do not necessarily mean that they are similar in all their attributes. Abu’l-Qāsim further differs from Nazzām in advocating the indestructibility of the atom. He holds that the atom had a beginning in time; but that it cannot be completely annihilated. The attribute of "Baqā" (continued existence), he says, does not give to its subject a new attribute other than existence; and the continuity of existence is not an additional attribute at all. The divine activity created the atom as well as its continued existence. Abu’l-Qāsim, however, admits that some atoms may not have been created for continued existence. He denies also the existence of any intervening space between different atoms, and holds, unlike other representatives of the school, that the essence or atom (Māhiyyat) could not remain essence in a state of non-existence. To advocate the opposite is a contradiction in terms. To say that the essence (which is essence because of the attribute of existence) could remain essence in a state of non-existence, is to say that the existent could remain existent in a state of non-existence. It is obvious that Abu’l-Qāsim here approaches the As̱ẖ‘arite theory of knowledge which dealt a serious blow to the Rationalist theory of matter. [53:5] In my treatment of the atomism of Islamic Rationalists, I am indebted to Arthur Biram's publication: "Kitābul Masā’il fil ḵẖilāf beyn al-Baṣriyyīn wal Bag̱ẖdādiyyīn". § II. Contemporary Movements of Thought. Side by side with the development of Mu‘tazilaism we see, as is natural in a period of great intellectual activity, many other tendencies of thought manifesting themselves in the philosophical and religious circles of Islam. Let us notice them briefly:-- 1. Scepticism. The tendency towards scepticism was the natural consequence of the purely dialectic method of Rationalism. Men such as Ibn As̱ẖras and Al-Jāhiz who apparently belonged to the Rationalist camp, were really sceptics. The standpoint of Al-Jāhiz who inclined to deistic naturalism[55:1], is that of a cultured man of the time, and not of a professional theologian. In him is noticeable also a reaction against the metaphysical hairsplitting of his predecessors, and a desire to widen the pale of theology for the sake of the illiterate who are incapable of reflecting on articles of faith.