No philosopher is without words about the human soul, because it is the closest thing to us, and to that closeness it is extremely mysterious. Ibn Sina sought knowledge of the soul since his early youth, because "whoever knows himself knows his Lord," as he told us in the treatise on psychic powers that he wrote for Prince Noah. Bin Mansour, it was his first book, and if Sheikh Al-Rais had begun his intellectual life with a treatise on the soul, he also concluded it forty years after writing that book, with a small treatise on the human soul, and in between during these years he composed many psychological treatises, as well as art. The sixth is from the natures of healing, and it is the book on the soul that is considered the most comprehensive of what has been written in this section.
The evidence of the importance of the Ainuist book of the soul, and of its great impact in the Middle Ages, is that it was translated into Latin, and spread widely among European philosophers. This is attested to by the forty-five remaining manuscripts of it in the libraries of Europe, and European thought has been subject to its influence since the twelfth century. Until the seventeenth century, when Descartes appeared and took his proof from Ibn Sina to prove the existence of the soul.