Word Meaning:
Atad- not real;
Mithyagyanam-false knowledge;
Viparyayaha-false knowledge.

Which is not established in the matter that false knowledge is Viparyaya.

Viparyaya means false knowledge. Therefore Viparyaya Vritti is untrue and is not accepted as a proof. For example— In the darkness with few lights we see a rope and doubtfully we consider the rope as a snake. But in fact neither the form of snake did not establish in the rope nor rope itself a snake. But to see the snake in the rope or in the rope we see the form of snake is Viparyaya Vritti i.e., false knowledge. This Vritti is not true and as such is not acceptable as a proof, because when the rope will be seen in the light then the false knowledge will be over and true knowledge is realized that this is rope and is not snake.

Therefore the Viparyaya Vritti of the Chitta is of false knowledge and cannot be considered as a proof. So we can say that the matter which is having its real form and if its real form is not seen in it, then it is called Viparyaya Vritti.
For-example- human body and whole matter of the world are mortal, but due to the attraction and being indulged in illusion we consider the same immortal.

It is due to Chitta’s Viparyaya Vritti which gives sorrows and if an aspirant become an ascetic knowing the word mortal and thus the aspirant starts worshipping God or practicing Ashtang Yoga, then this is Chitta’s Aklishta Viparyaya Vritti which gives no sorrows. We must always think that our forefathers have gone to the final resting place but could not take a single pie with them. But due to the effect of this Klishta Viparyaya Vritti up till the point of death the man or woman remains after the materialistic world. So the Yoga Practice enables an aspirant to remove the effect of Klishta Viparyaya Vritti for attaining Salvation. The description of Vikalpa Vritti will follow.