When the Romans began to raid the Greek Empire, many scholars fled to parts of the Arab world, taking with them classic works of arts and philosophy. Later, with the fall of Rome to the Goths in 410 and the death of Augustine in 430, the Western world entered the Dark Ages that lasted for six centuries. Supernatural explanations and anti-intellectualism prevailed, and the church and its dogma was all powerful. At the same time, Islam was expanding rapidly, eventually encompassing an area even greater than the Roman Empire at its peak. This expansion brought the Arabs into contact with ancient works lost to the Western world, of special interest to them because of their practical value. Arab philosophers translated and studied these works, especially Aristotle (384-322 B.C.).

Avicenna (Arabic name: Ibn Sina), born at Afshana near Bukhara (Central Asia), was a child prodigy, a physician before he was 20, and wrote books on many topics. His major contribution to medical science was his book The Canon, an immense encyclopedia of over one million words. He also made major contributions to astronomy, physics, chemistry, and music. He was heavily influenced by Aristotle's philosophy (in adolescence he had read Aristotle's Metaphysics forty times) and the revisions he made to it were to become the standard for hundreds of years. One modification concerns the number of senses we possess: for Aristotle, in addition to the five external senses, we have three internal senses (common sense, imagination, memory); for Avicenna, there are seven hierarchical internal senses (from bottom to top: common sense, retentive imagination, composite animal imagination, composite human imagination, estimative power, the ability to remember outcomes of lower processes, the ability to use that information). His major departure from Aristotle involved the active intellect: for Aristotle, the active intellect was employed for understanding universal principles beyond the scope of empirical observation; for Avicenna, it was used for understanding God, the highest level of knowledge. He believed that knowledge is best attained through mystical illumination. Avicenna's work is said to have made possible the philosophical achievements of 12th and 13th century Europe (Scholasticism).