By which duty (dharma) and lawlessness (adharma), and what ought to be done and what ought not to be done, One understands incorrectly, that understanding (buddhi), O son of Pritha (Pārtha), is of passion (rājasī).
When one fails to discern sacred duty from chaos, right acts from wrong, understanding is passionate.
(31) The intellect by which lawful-right and lawless-wrong, what should be done and what should not, are untruly understood, is [an intellect] in Passion's way.
18.31 O Pārtha, that intellect is born of rajas with which one wrongly understands virtue and vice as also what ought to be done and ought not to be done.
18.31 The Buddhi which gives an erroneous knowledge of Dharma and Adharma (its opposite) and also of what ought to be done and what ought not to be done, O Arjuna, is Rajasika.
18.31 That, by which one wrongly understands Dharma and Adharma and also what ought to be done and what ought not to be done -- that intellect, O Arjuna, is Rajasic (passionate).