Sanskrit
अधर्मं धर्ममिति या मन्यते तमसा वृता । सर्वार्थान् विपरीतांश्च बुद्धिः सा पार्थ तामसी ॥ ३२ ॥
adharmaṃ dharmam iti yā manyate tamasā vṛtā sarvārthān viparītāṃś ca buddhiḥ sā pārtha tāmasī
Translation
That which, enwrapped in darkness, thinketh wrong to be right and seeth all things subverted, that Reason, O Partha, is of darkness.
Annie Besant · The Bhagavad-Gita, translated by Annie Besant (4th ed., 1922) — Wikisource · Public Domain
Explanation
Tamasic buddhi goes further than confusion into outright inversion — wrapped in darkness, it takes wrong for right and sees everything “subverted.” This is the sharpest of the three failures and completes a clean gradient: sattva discriminates correctly, rajas discriminates unreliably, tamas discriminates backwards.