Four type of learning itself means Kautilya - (1) आन्वीक्षिकी the learning exposing truth through proper examination (2) त्रयी means the three Veda - Regveda, Yajurveda and Samveda (3) वार्ता means agriculture, cattle rearing and trade and commerce (4) दण्डनीति contains provisions for punishment to criminals. It is meant for the welfare of people.
The disciples of Usanasa accept दण्डनीति only. The disciples of Brihaspati accept two type of learning वार्ता and दण्डनीति. While त्रयी, वार्ता and दण्डनीति are accepted by the disciples of Manu. On the contrary, the disciples of Kautilya accept four types of learning - (1) आन्वीक्षिकी (2) त्रयी (3) वार्ता and (4) दण्डनीति