Concept:
The concept of Avijñapti-rūpa (unmanifest form) is a unique and sophisticated ontological category used to explain how an ethical action (Kamma) continues to "exist" within a person even after the physical act has ended, but before the result (Vipaka) has ripened. It is a bridge between physical action and moral consequence.
Step 1: The Vaibhāṣika perspective on moral persistence.
The Vaibhāṣika school (a branch of Sarvāstivāda) held that when one makes a vow or performs a significant moral act, a subtle "physical" (rūpa) entity is created. It is called *Avijñapti* because it is "unmanifest"—it cannot be seen or felt by others—but it is considered "material" in nature. This unmanifest form persists in the stream of the individual, ensuring that the moral potential of the act is preserved.
Step 2: Contrast with other schools.
The Sautrāntikas rejected this "unmanifest matter," preferring the theory of "seeds" (Bija) in the mind. The Vijñānavāda (Yogacara) school internalized all such processes into consciousness (Alayavijñana), and the Mādhyamika school focused on the emptiness (Shunyata) of all such constructs. Thus, *Avijñapti* is a distinctively Vaibhāṣika technical term.