BG 14.8

14.8 तमः inertia? तु but? अज्ञानजम् born of ignorance? विद्धि know? मोहनम् deluding? सर्वदेहिनाम् to all,embodied beings? प्रमादालस्यनिद्राभिः by heedlessness? indolence and sleep? तत् that? निबध्नाति binds fast? भारत O descendant of Bharata (Arjuna).Commentary Tamas is that binding force with a tendency to lethargy? sloth and foolish actions. It causes delusion or nondiscrimination. It binds him who associates the Self with the body. A Tamasic man acts under the compulsion of the wants of the body. He has no power of judgment. Troubled by the wants of the body he acts under pressure to keep himself alive. His actions are not guided by reason. They are on the plane of instinct. His senses are dull. He becomes infatuated and stupefied. He has no inclination to work. He yawns much. He sleeps too much. He always wants to sleep. He nevr knows when and how to act? what? to whom and how to talk. He takes delight in following the wrong path. He does not know how to behave or how to address others. He is thoughtless and ignorant. He forgets everything. He is negligent and indolent. He is just in a stage higher than lifeless matter.He who is under the grip of heedlessness (Pramada) is not able to discriminate between the eternal and the noneternal. This is an enemy of illumination? the effect of Sattva. He who is overpowered by laziness (Alasya) is not able to exert. This is an enemy of Pravritti? the effect of Rajas. Sleep (Nidra) is LayaVritti? (a state of absorption into ignorance) which is dependent on Tamas. This is the enemy of the works done by Sattva and Rajas.

— vedicscriptures · exposition · source ↗

In this verse the specific application of the word tu is very significant. This means that the mode of ignorance is a very peculiar qualification of the embodied soul. The mode of ignorance is just the opposite of the mode of goodness. In the mode of goodness, by development of knowledge, one can understand what is what, but the mode of ignorance is just the opposite. Everyone under the spell of the mode of ignorance becomes mad, and a madman cannot understand what is what. Instead of making advancement, one becomes degraded. The definition of the mode of ignorance is stated in the Vedic literature. Vastu-yāthātmya-jñānāvarakaṁ viparyaya-jñāna-janakaṁ tamaḥ: under the spell of ignorance, one cannot understand a thing as it is. For example, everyone can see that his grandfather has died and therefore he will also die; man is mortal. The children that he conceives will also die. So death is sure. Still, people are madly accumulating money and working very hard all day and night, not caring for the eternal spirit. This is madness. In their madness, they are very reluctant to make advancement in spiritual understanding. Such people are very lazy. When they are invited to associate for spiritual understanding, they are not much interested. They are not even active like the man who is controlled by the mode of passion. Thus another symptom of one embedded in the mode of ignorance is that he sleeps more than is required. Six hours of sleep is sufficient, but a man in the mode of ignorance sleeps at least ten or twelve hours a day. Such a man appears to be always dejected and is addicted to intoxicants and sleeping. These are the symptoms of a person conditioned by the mode of ignorance.

— vedicscriptures · exposition · source ↗