(1) Wisdom.  (2) Mind.  (3) Intellect. Capacity to understand the essence of the Shaastra.

The word Buddhi means that which gives the power of perception, understanding and discrimination. Buddhi is the faculty of individualized consciousness that is responsible for processing various pieces of available information, making various decisions regarding the interactions between various components of the Antahkaran (heart). Buddhi operates within the limits of current destiny and its decisions shape future destiny.

There are different functions of Buddhi. A high level block within Buddhi influences the decision-making faculty of Buddhi based on information from Chitta (conditioning). The decision-making faculty within Buddhi itself is controlled by Jupiter while transmitting those decisions to Chitta and Manas is done by Mercury.

Understanding (feeling) information from input channels of Manas (sensory and motor mind) : Mercury (aided by Moon)
--Deciding what information to retrieve from Chitta (memory and conditioning) : Jupiter
--Retrieving and storing information from Chitta (memory and conditioning) : Mercury
--Deciding what information to store to Chitta (memory and conditioning) : Jupiter
--Deciding what commands to send to output channels of Manas (sensory/motor mind) : Jupiter
--Sending commands to output channels of Manas (sensory and motor mind) : Mercury (aided by Moon)