सुपि स्थः

The affix क comes after the root स्था when in composition with a word ending in a case-affix, as an उपपद ।
In the three previous sutras, the word in composition was always in the accusative case. This sutra declares that with regard to the verb स्था, the upapada may have any case not necessarily the accusative. As समस्थः = समे तिष्ठति 'who dwells in accessible position'; and विषमस्थः 'having an inaccessible position'.

This sutra should be divided into two sutras (yoga-bibhaga). Thus:- (1) सूपि ॥ The affix क comes after every root ending in long आ, when in composition with a case-inflected word; as द्वाभ्यां पिबति = द्वि + पा + क = द्विपः 6.4.64 'who drinks with two organs' i.e. 'the proboscis and the mouth, an elephant'. So also पादपः 'a plant' (what drinks through the foot). कच्छपः 'a tortoise' (that always protects its mouth by drawing it in, at the approach of danger). (2) सूपिस्थः ॥ The affix क comes after the root स्था when in composition with a word ending in a case-affix. Why do we make this two-fold division, when we see the second rule is included in the first as the verb स्था also ends in a long आ ? The reason is that the first rule applies where the agent is indicated, while the second rule applies where condition is to be denoted. As आखूनामुत्थानम् = आखूत्थः 'a swarm of rats'; so also शलमोत्थः ' a swarm of locusts'.

Both the words कर्मणि and सुपि are understood in the sutras that follow: vis: the word कर्मणि in sutras that relate to transitive verbs, and the word सुपि everywhere else.