In early Islamic thought, which refers to philosophy during the "Islamic Golden Age", traditionally dated between the 8th and 12th centuries, two main currents may be distinguished. The first is Kalam, that mainly dealt with Islamic theological questions, and the other is Falsafa, that was founded on interpretations of Aristotelianism and Neoplatonism. There were attempts by later philosopher-theologians at harmonizing both trends, notably by Avicenna who founded the school of Avicennism, Averroes who founded the school of Averroism, and others such as Ibn al-Haytham (Alhacen), Abū Rayhān al-Bīrūnī.
Some differences between Kalam and Falsafa
Aristotle attempted to demonstrate the unity of God; but from the view which he maintained, that matter was eternal, it followed that God could not be the Creator of the world. To assert that God's knowledge extends only to the general laws of the universe, and not to individual and accidental things, is tantamount to denying prophecy. One other point shocked the faith of the Mutakallamin — the theory of intellect. The Peripatetics taught that the human soul was only an aptitude — a faculty capable of attaining every variety of passive perfection — and that through information and virtue it became qualified for union with the active intellect, which latter emanates from God. To admit this theory would be to deny the immortality of the soul. 
Wherefore the Mutakallamin had, before anything else, to establish a system of philosophy to demonstrate the creation of matter, and they adopted to that end the theory of atoms as enunciated by Democritus. They taught that atoms possess neither quantity nor extension. Originally atoms were created by God, and are created now as occasion seems to require. Bodies come into existence or die, through the aggregation or the sunderance of these atoms. But this theory did not remove the objections of philosophy to a creation of matter.
For, indeed, if it be supposed that God commenced His work at a certain definite time by His "will," and for a certain definite object, it must be admitted that He was imperfect before accomplishing His will, or before attaining His object. In order to obviate this difficulty, the Motekallamin extended their theory of the atoms to Time, and claimed that just as Space is constituted of atoms and vacuum, Time, likewise, is constituted of small indivisible moments. The creation of the world once established, it was an easy matter for them to demonstrate the existence of a Creator, and that God is unique, omnipotent, and omniscient.
