Manas literally means mind. The mind connects and co-ordinates the five senses of perception and five organs of action. At the same time it acts as the inner-most sense(antarendriya), the agent connecting the buddhi and ahamkara with the purusa. The mind plays a double role. Its role is to connect the 10 indriyas on the one hand, and, on the other, to connect the intelligence, consciousness and the core. This dual role of the mind affects the chitta so that it plays a double role. The mind being the gross part of consciousness needs to distinguish between subject and object.
Buddhi literally means wisdom or intelligence. Buddhi is another component of chitta. It is an instrument that acts as the true assessor. It helps to acquire the reliable and untainted knowledge that comes from experience. Its power of discernment is the lusture of wisdom. Buddhi is the axial constituent of chitta. It acts as a gravitational force to draw the chitta towards the seer. It is the mediator. It is the judging faculty that orientates the other instruments on the inner-path. Like consciousness, intelligence too is tied on the threshold between wordly pleasures and liberation from them.
Purusa is the self, or the seer. Purusa the Lord of the body, is called the atman, the seer, the self, the soul. Patanjali calls the seer chiti shakthi. As the body is the supporter of consciousness, consciousness is the foundation or base for the purusa to realise his position and status. As chitta has its own dispostion, purusa too has his own significant nature. Purusa, atman or the seer, does not rely on nature. It cannot involute. In order to feel the purusa, one has to reach its final destination-i.e., its evolution and culmination. Intelligence acts as a bridge in connecting the consciousness of nature with the consciousness of the seer.