Nyāya Sūtras 2.29

2.29

tattvajñānaviṣayasya vibhāgāt tattvajñānāya kalpate tarka iti/ so 'yam itthambhūtas tarkaḥ pramāṇasahito vāde sādhanāyopālambhāya cārthasya bhavatīty evam arthaṃ pṛghag ucyate prameyāntarbhūto 'pīti/

because of the distinction of the object of knowledge of reality, hypothetical reasoning serves for the knowledge of reality. Being of this nature, hypothetical reasoning, accompanied by the means of valid cognition, serves for the establishment and censure of an object in a philosophical debate; for this purpose it is mentioned separately, even though it is included within the object of valid cognition.