The most concentrated statement in the Upanishads of Brahman as the enabling ground of all faculties. Not an object of knowledge — but what makes knowing possible. Know that alone as Brahman, not this which people here worship.
Verse 1.4 is the pivot of the first section, applying the same logic from verses 1.1–2 to the mind directly. The mind can think many things. It can even think about Brahman — forming a concept, constructing a description, imagining something very large or very wise or very infinite. But whatever the mind can think is an object of the mind, not the ground of the mind.
Brahman is what the mind does not think — not because Brahman is absent or unknowable in principle, but because the mind cannot contain its own ground the way an eye cannot see itself. The thinking happens in consciousness. Consciousness is not a thought within thinking.
The last line is striking: not this which people here worship. It is not a rejection of devotional practice. It is a clarification: whatever can be made into an object of worship is not the final Brahman. A deity, a concept, a symbol — all of these are within consciousness. What the verse points at is prior to all of them.
The verse uses the same structural pattern as verses 1.3 (eye), and by implication 1.1–2 (mind, breath, speech, hearing). For each faculty: Brahman is not what that faculty grasps — it is what enables that faculty to grasp at all. This is the Kena's systematic application of the via negativa not just to descriptions of Brahman but to the faculties of knowing themselves.
The phrase yenahur mano matam — by which the mind is said to be known as mind — is precise. The mind is made to be mind, made to have its mind-nature, by something prior to it. That prior something is what is being pointed at. It cannot be approached as an object of knowledge because all objects of knowledge appear within it.
Neda yad idam upāsate — not this which people worship here. Śaṅkara reads this as a sharp distinction between Saguṇa Brahman (Brahman with attributes, approached through devotion) and Nirguṇa Brahman (Brahman without attributes — the absolute). Devotional objects — however sublime — are still objects within consciousness. Verse 1.4 points past all objects to their ground. The verse is not dismissing upāsanā but locating it: useful, necessary as preparation, but not the final recognition.
Śaṅkara's Kena Bhāṣya distinguishes two possible readings of verse 1.4. The first reading (prathamapakṣa): the verse teaches that Brahman is the inner controller of the mind — consciousness that controls the mind from within, distinct from the individual mind though not separate from it. The second reading (siddhānta): the verse points to the absolute identity of Brahman and the witness-consciousness — not a relationship of controller to controlled, but of ground to appearance. Śaṅkara adopts the second reading as the final position: Brahman is not a further entity that does something to the mind; Brahman is what the mind ultimately is when correctly understood as pure consciousness rather than as a cognitive instrument.
In the Upadeśasāhasrī (authenticated as Śaṅkara's own by Sengaku Mayeda), the structure of Kena 1.4 is the template for the central pedagogical method: the teacher presents Brahman successively as not-eye, not-mind, not-speech — exhausting the student's habit of locating Brahman among objects — and then, when the student's conceptual reaching has been stilled, delivers the positive pointing: that by which. The negative and positive are not sequential steps but simultaneous movements: the negation of the wrong identification and the recognition of the right one happen together. Kena 1.4 performs this in a single verse.
Kena 1.4 is structurally related to the Bṛhadāraṇyaka's Neti Neti passages (BAU 2.3.6, 3.9.26) but differs in one important respect: the Bṛhadāraṇyaka negates descriptions of Brahman, while Kena 1.4 negates the faculties of knowing themselves. Both perform the same function — clearing inadequate approaches — but the Kena's approach is more radical. It does not just say Brahman is not this-or-that description; it says Brahman is not an object of any faculty whatsoever. This takes the via negativa from the object domain into the epistemological domain itself.