In Vedic philosophy, Rta is the most important concept as it is the cosmic, eternal, and moral order. Rta means the basic truth, harmony, or universal system that no one is allowed to break. Rta means Truth of Truths, which is also called Satyasya Satyam. Rta is the eternal and unbreakable law of nature. Rotation of Heavenly stars, alteration of day and nights, the flow of rivers, oceans, etc. are controlled by Rta. Rta makes sure that everything remains in its correct place.
The principle of Rta is immortal and everywhere. It is inherent in all the works of Cosmos. Rta is the limiting principle of this cosmos, whether physical or moral.
Arthapatti in Indian philosophy means the fifth of the five means of knowledge through which one gets correct awareness of the world. Arthapatti is that which is received through an organized fact. Arthapatti, which is also called postulation, is a required idea of an unperceived fact that alone can describe a phenomenon that requires an explanation. For example, a man who fasts during the day grows fat. Fasting and Fatness cannot be accommodated together unless we admit that the man eats during the night. This postulation is known as Arthapatti. It is the type of reasoning that allows us to reason with the facts.