Vyapti is considered as the ground of inferences. The conclusion cannot be inferred logically without the knowledge of vyapti.
Vyapti is expressed by the help of a general or universal statement. This universal statement expresses the relation of constant concomitance (Niyata sahacarya) between the middle team (hetu) and the major term (sadhya).
In other words vyapti implies the knowledge of invariable relation of causality or co-existence (sahacara) between sadhya and hetu (in all the past, present and future instances).
Such knowledge is possible when we know that there is the relation of unconditionality (anupadhik sambandha) between the two. Thus vyapti has been defined as the unconditional and constant concomitant relation between vyapya and vyapaka (pervaded and pervader).
In the example of the five stepped argument discussed earlier, the third step ascertains the relation of vyapti. It is essential for any inference in the Indian logical pattern.