In this world there are some objects that are perceptible and some imperceptible. Among them each subject is unique. Its inherent properties are distinct. An investigation into the nature of these objects is philosophy or ‘darshanas’.

These ‘darshanas’ are mainly two-fold. They are ‘aastika’ and ‘naastika’ (Orthodox and Heterodox). Here the terms ‘aastika’ and ‘naastika’ which does not, however, mean those who accept existence of bhagavaan/God and those who donot. This orthodox-heterodox terminology is a construct of Western languages and lacks scholarly roots in samskrit. According to Andrew Nicholson, there have been various heresiological translations of aastika and naastika in 20th century literature on sanaatanadharma but quite many are unsophisticated and flawed.

Ancient and medieval era texts of sanaatanadharma include extensive discussions on ontology (metaphysics, brahma–aatmaa, soonyata–ananta), reliable means of knowledge (epistemology, pramaanas), value system (axiology) and other topics.

‘aastika-darshana’ is that which accepts the authority/praamaanya of the vedas and

‘naastika-darshana’ is that which do not accept the authority/pramaanya of the vedas.

Six aastika darshanas of vedic literature.

… Provide the reality in six different perspectives of the universe.

…The six darshanas are nyaaya, vaisheshika, saankhya, yoga, meemaasa and vedaanta.

The 6 orthodox systems of bhaarateeya philosophy, popularly known as shaddarshanas are saankhya and yoga, vaisheshika and nyaaya. poorvameemaamsa and uttarameemaamsa (or vedaanta). These have been traditionally recognised as 3 pairs because of some affinity in thought between them, (though each flourished independently with individuality often attacking others like friendly quarrels among brothers of a joint family). They were intended to help the interpretation of vedic texts believed to be the revelation of paramaatmaa, thus called aastika darshanas. Despite differences in their doctrines and methods, one thing is common to all the orthodox systems namely that liberation/salvation/moksha is the sole end and aim of life with knowledge as the door leading to it. The sages/rushis (sootrakaaras) first codified the findings in each system as sootras which later scholars have built up imposing superstructures with their commentaries called bhaashya, vaartika, vrutti, vyaakhya, teeka etc., as detailed below:

In contrast to aastikadarshanas, naaastika systems/naastika darshanas are like the chaarvakas (brihaspati/chaarvaka), the Buddhists (Gautama Buddha) and the Jains (Rushabadeva/Mahaviraswamy), who do not believe in the authority of Vedas and existence of Paramaatmaa.