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In this paper, the importance of perception and assertion as the basic elements of cognition is discussed. Perception and assertion, which are taken from Greek philosophical heritage, have been accepted by most of the Islamic scholars and philosophers. These two concepts, though very important, are not very clear in understanding. The author believes if the way of looking at these concepts changes, it can solve many problems. What is argued in this article is that, in contrast with the common belief, perception is a kind of assertion. In other words, what is acceptable for human being is only assertion. That is what takes place in ontological and epistemological dimension is assertion. This assertion is either the assertion of "what is" or then the assertion of "relationship of something to the other." With this interpretation, assertion is categorized in action and the self (soul) in knowing things acts actively. In proposition, we must look at the subjects of the clauses not to the clauses themselves. The propositions can get the adjectives of correspondence and non correspondence. Knowledge takes place if anything presents itself before the self – conscious of self, if it accepts it. This acceptance is a kind of action. Meanwhile, wisdom is present, observes everything, and confirms this action. Thus, the perception and assertion are kinds of Self (soul)’s actions and are categorized in possession category.