That which thinks adharma is dharma, enveloped in darkness, and all things opposite — that intelligence is tāmasic, oh Pārtha.

Tāmasic intelligence: tamasā āvṛtā — enveloped by tamas (darkness). Complete winter of the mind.

Adharmam dharmam iti manyate — thinks that which is incorrect is correct. Sees sarvārthān viparītān — all things opposite, reversed. There is no discrimination, only confusion.