 Perhaps most original in Dignāga’s work on argument and inference is what he called the wheel of reasons (hetu-cakra), an equivalent alternative to the three forms of reason (tri-rūpa-hetu). It comprises a three by three matrix, which distinguishes a proper from an improper reason. It specifies, on the one hand, the three cases of the reason (hetu) occurring in some, none, or all of subject-like things (sa-pakṣa), and, on the other, the three cases of the reason (hetu) occurring in some, none, or all of subject-unlike things (vi-pakṣa). Letting H be the reason, S the subject-like things and \(\bar{\mbox{S}}\) the subject-unlike things, we obtain the following table.