This is a chapter from De Lacy O'Leary's 1922 scholarly history of Islamic philosophy, tracing how Aristotelian thought entered the Arab world via Syriac translations and was subsequently developed by a distinct lineage of Arabic philosopher-scholars called the *falasifa*. The central argument is that this transmission was neither passive nor merely derivative: the *falasifa* actively corrected and extended Aristotle by working from Greek sources and neo-Platonic commentators, and in doing so became the primary conduit through which Aristotelianism later reached Latin Christendom. The chapter focuses closely on al-Kindi (d. 873 AD), the founding figure of this tradition, detailing his four-faculty theory of intellect — three internal to the soul, one an "Agent Intellect" emanating from God — which he derived from Aristotle's *De Anima* as filtered through Alexander of Aphrodisias and the pseudo-Aristotelian *Theology* (actually an abridgment of Plotinus). A notable historiographical claim O'Leary makes is that the supposed "lack of originality" in Arabic philosophy is a misconception rooted in ethnic bias, since most leading Islamic philosophers were Persian, Turkish, or Berber — not Arab or Semitic — and the real constraint was simply that Greek psychological theory had no serious rivals until modern natural science. The chapter positions al-Kindi as the crucial selector of starting-points: his choices about which Aristotelian problems to foreground — especially in psychology and metaphysics — set the agenda that all subsequent *falasifa* would follow.