The words pra etc. are called nipāta when not signifying substances.,
The following is the list of प्रादयः or 'prepositions:' प्र, परा, अव, सम्, अनु, अव, निस्, दुस्, वि, आङ्, नि, अधि, अपि, अति, सु, उत्, अभि, प्रति, परि, उप ॥
The making of this a distinct aphorism, when it could well have been included in the last, is for the sake of giving the Pra &c., words two names, namely, those of Nipatas, as well as upasargas under certain circumstances, i.e., when they are in composition with verbs. Not so however the cha &c., words. They never get the designation of upasargas.
When these words signifying substances they are not Nipatas. As परा जयति सेना the excellent army conquers. Here the word परा is not a Nipata.,