In Arabic language, the word aql (intellect)and its derivatives denoted special concepts prior to the revelation of the Quran. Referring to the views of philologists and Arabic poetry, these concepts will be analyzed in the present paper. Then,examining the concept of aql (intellect) in the Holy Quran as a semantic field and the best syntagmatic andsynonymous concepts and their paradigms and relying on Sheikh Tusi’s invaluable al-Tebyan Interpretation, the functions of aql will be explained.