Sage Bharata is the author of the work called Natyasastram. He had written it probably in the 4th Century BC. This is the oldest and existing work on Indian Dance, Dramaturgy and Poetics.

Bharata enumerates eight sentiments or Rasas in his work without dealing elaborately with Santa rasa or the sentiment of Calm as the ninth. Later writers of Indian poetics gave importance to Santa rasa and said that the sentiments are nine in number.

The nine sentiments are Sringara (Erotic), Karuna (Pathos), Raudra (Fierce), Vira (Heroic), Bhayanaka (Fright), Hasya (Laughter), Bibhatsa (Odious), Adbhuta (Wonderment) and Santa (Calm).

Each of the above sentiments has a Sthayibhava or a predominant state of mind. This predominant state of mind has to exist for the particular Rasa to survive. For example, Sringara Rasa has Rati as its Sthayibhava and this Rati has to exist for Sringara Rasa to survive! Thus there are nine Sthayibhavas as well. Each Rasa has its own Sthayibhava as follows:

Sringara - Rati

Karuna - Shoka

Raudra - Krodha

Vira - Utsaha

Bhayanaka - Bhaya

Hasya - Hasa

Bibhatsa - Jugupsa

Adbhuta - Vismaya

Santa - Shama

It is believed that all the nine sentiments are permanent in an individual but only one of them manifests at a given point of time while the rest remain covered by a 'Screen'!