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The wise man Knows that there is Knowledge higher that his, and this
causes him to be humble, while the ignora1ll one thinks that there is no limit for his Knowledge.
(al-Kindi, 185-252 A.H.)
Etplaining the reality of Knowledge and the way to access to the most truth is among the interesting issues. to which the philosophers, since the ve')' begining of philosophy. have paid attelition, and feel themselves compelled to discuss this issue. Yet, it is among the unsolved philosophical enigmas. In the Islamic philosophy, this problem is approached from the angle of the relation between perception and perceived thing 011 the one hand, and the relation between the perception and perceiving thing 011 the
other. Taking the definition of Knowledge as the illustration of the realiy of object or the presence of the quiddity of object in perciving one, this issue has always faced the well-known problem of association between substance and accident. This cause many theories to appear: J) the theo')' of quality of correlated essence;2)
the tlleo')' of image; 3) the tlleo')'. in which quiddity is employed to provide various explications.

In the present article,after discussing the developmellt of the doctrines of Muslim philosophers, the author will go 011 to analyze each one of these theories, and will explain their persumptions, the factors which are of influence in their development, the objection adduced against them in terms of standards such as consistency, independence, and completeness, and their resistance against the skeptic attacks.