Avicenna was not quite certain in many of existential problems and arbitrary sciences. This is not out of his weakness, but because of his utmost fairness and humility. His views on religious issues, including resurrection, indicates his being after finding the truth which is without exaggeration. Besides, as far as mystical issues are concerned, he is careful not to have any idealistic tendencies in scientific and philosophical matters. In the following paper, the author tries to emphasize on the point that Avicenna thinks systematically even in philosophizing, and approaches the matters with caution and wise humility. Finally, he mentions two of Avicenna’s works named al-Ensāf and a major part of Hekmat al-Mashreqin, which is lost.