Theoretical knowledge about realities is quite different from direct understanding of the characteristics of realities which are appearing. These are two different levels of understanding. We may, for example, speak now about seeing as reality, a kind of nama which is not self, an element which experience visible object. When someone speaks about the nature of seeing but he is not yet aware of the characteristic of seeing while there is seeing, there is merely understanding on the level of thinking, thus, theoretical understanding stems from listening and considering what one hears. It is important to consider and investigate the Dhamma one hears, this is a necessary foundation for right understanding. The understanding which stems from listening is accumulated and this accumulated understanding is a condition for the arising of direct awareness later on. Then there can be awareness of seeing when it presents itself and at such a moment direct understanding of its characteristic can develop; seeing can be understood as a reality, as only an element, not self.