▁are ▁class ified ▁as ▁either ▁orth odox ▁or ▁heter odox ▁– ▁ ā st ika ▁or ▁n ā st ika ▁– ▁depending ▁on ▁one ▁of ▁three ▁alternate ▁criteria : ▁whether ▁it ▁bel ieves ▁the ▁V ed as ▁are ▁a ▁valid ▁source ▁of ▁knowledge ; ▁whether ▁the ▁school ▁bel ieves ▁in ▁the ▁prem ises ▁of ▁Bra h man ▁and ▁At man ; ▁and ▁whether ▁the ▁school ▁bel ieves ▁in ▁after life ▁and ▁De vas . ▁ ▁There ▁are ▁six ▁major ▁schools ▁of ▁orth odox ▁Indian ▁H indu ▁philosophy — N y aya , ▁Va ish esh ika , ▁Sam kh ya , ▁Y oga , ▁M ī m ā ṃ s ā ▁and ▁V ed anta , ▁and ▁five ▁major ▁heter odox ▁schools — J ain , ▁Buddh ist , ▁A j iv ika , ▁A j ñ ana , ▁and ▁C ā rv ā ka . ▁However , ▁there ▁are ▁other ▁methods ▁of ▁classification ; ▁Vid yar anya ▁for ▁instance ▁ident ifies ▁six teen ▁schools ▁of ▁H indu ▁Indian ▁philosophy ▁by ▁including ▁those ▁that ▁belong ▁to ▁the ▁Ś a iva ▁and ▁R ase ś var a ▁trad itions . ▁ ▁Each ▁school ▁of ▁H indu ▁philosophy ▁has ▁extensive ▁ep ist em ological ▁literature ▁called ▁Pr am ana - s astr as . ▁ ▁In ▁H indu ▁history , ▁the ▁distinction ▁of ▁the ▁six ▁orth odox ▁schools ▁was ▁current ▁in ▁the ▁Gu pta ▁period ▁" g old en ▁age " ▁of ▁H indu ism . ▁With ▁the ▁disapp earance ▁of ▁Va ish esh ika