In plain words
But that knowledge which clings to one limited effect as though it were the whole, without reason, missing the truth and narrow in scope, is declared tāmasa.
Word for word
But that which is attached to one effect as if it were the whole, without reason, without a true object and trivial, that is declared tāmasa.
यत्तु कृत्स्नवदेकस्मिन् कार्ये सक्तमहैतुकम्अतत्त्वार्थवदल्पं च तत्तामसमुदाहृतम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
यत् ज्ञानं कृत्स्नवत् समस्तवत् सर्वविषयमिव एकस्मिन् कार्ये देहे बहिर्वा प्रतिमादौ सक्तम् ‘एतावानेव आत्मा ईश्वरो वा, न अतः परम् अस्ति’ इति, यथा नग्नक्षपणकादीनां शरीरान्तर्वर्ती देहपरिमाणो जीवः, ईश्वरो वा पाषाणदार्वादिमात्रम् , इत्येवम् एकस्मिन् कार्ये सक्तम् अहैतुकं हेतुवर्जितं निर्युक्तिकम् , अतत्त्वार्थवत् अयथाभूतार्थवत् , यथाभूतः अर्थः तत्त्वार्थः, सः अस्य ज्ञेयभूतः अस्तीति तत्त्वार्थवत् , न तत्त्वार्थवत् अतत्त्वार्थवत् ; अहैतुकत्वादेव अल्पं च, अल्पविषयत्वात् अल्पफलत्वाद्वा । तत् तामसम् उदाहृतम् । तामसानां हि प्राणिनाम् अविवेकिनाम् ईदृशं ज्ञानं दृश्यते ॥ २२ ॥
In plain words
Knowledge that treats a single, limited effect — say, the body, or, outwardly, some image — as if it were everything, as if it were the whole; thinking 'this much alone is the Self, or God; nothing beyond this exists' — like naked ascetics who take the Self to exist only within the body, exactly body-sized, nothing more than the individual soul; or like someone who takes God to be nothing but stone or wood. Fixed like this on one narrow thing, without any real grounding, devoid of reason, with no logical justification, this knowledge fails to grasp anything actually real — its object isn't things as they truly are. 'As it truly is' is what 'a true object' properly means — the thing that would actually be there to know, if the knowledge were sound; but this knowledge does not have a true object, it merely seems to. Precisely because it lacks any rational basis, and because its scope is so narrow, or its fruit so meager, this kind of knowledge is cited as an example of the tamasic type. Such knowledge is exactly what one sees, indeed, among tamasic, undiscriminating creatures.
Close to the Sanskrit
The knowledge which, as if entire, as though complete, as if having everything as its object, is fixed on one single effect — the body, or, externally, on an image and the like — thinking 'this much alone is the Self, or the Lord; nothing beyond this exists' — just as, for naked ascetics and the like, the Self exists within the body, having the exact measure of the body, the individual soul; or the Lord is merely stone, wood, and the like — thus, fixed on one single effect, without a rational basis, devoid of reason, without logical justification, as though not having a true object, as though its object were not as it actually is — 'as it truly is' is the object, that is the true object; that, being the object of knowledge for this knowledge if sound, would exist — thus is 'having a true object'; not 'having a true object', but 'as though not having a true object'; because of being without rational basis alone, and meager, because of having a limited scope, or because of yielding a limited fruit — that is exemplified as tamasic. For indeed, among tamasic, undiscriminating living beings, such knowledge is seen.