The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
50. On account of the connexion and so on (the agnis built, of mind, &c. are independent); in the same way as other cognitions are separate. And there is seen (another case of something having to be withdrawn from the leading subject-matter); this has been explained (in the Pûrva Mîmâmsâ-sûtras).
Independence has, against the general subject-matter, to be assumed for the fire-altars built of mind and so on, for that reason also that the text connects the constituent
members of the sacrificial action with activities of the mind, &c.; viz. in the passage, 'With mind only they are established, with mind only they are piled, with mind only the cups were taken, with mind the udgâtris praised, with mind the hotris recited; whatever work is done at the sacrifice, whatever sacrificial work, was done as consisting of mind, by mind only, at those fire-altars made of mind, piled by mind,' &c. For that connexion has for its result an imaginative combination (of certain mental energies with the parts of the sacrifice), and the obtainment of the parts of the sacrifice which are objects of actual perception cannot be made dependent on such imaginative combination 1. Nor must it be supposed that, because here also, as in the case of the meditation on the udgîtha, the vidyâ is connected with members of the sacrificial action, it enters into that action as a constituent part; for the statements of the text differ in the two cases. For in our case scripture does not say that we are to take some member of a sacrificial action and then to superimpose upon it such and such a name; but rather takes six and thirty thousand different energies of the mind and identifies them with the fire-altars, the cups, and so on, just as in some other place it teaches a meditation on man viewed as the sacrifice. The number given by the text is originally observed as belonging to the days of a man's life, and is then transferred to the mental energies connected therewith.--From the connexion (referred to in the Sûtra) it therefore follows that the agnis piled of mind, &c. are independent.--The clause 'and so on' (met with in the Sûtra) must be explained as comprehending 'transference' and the like as far as possible. For if the text says, 'Each of those Agnis is as great as that prior one,' it transfers the glory of the fire-altar consisting of the work (i.e. the real altar piled of bricks) to the altars consisting of knowledge and so on, and thereby
expresses want of regard for the work. Nor can it be said that if there is connexion (of all the agnis) with the sacrificial action, the later ones (i.e. those made of mind) may optionally be used instead of the original agnis made of bricks (as was asserted by the pûrvapakshin in Sûtra 45). For the later agnis are incapable of assisting the sacrificial action by means of those energies with which the original agni assists it, viz. by bearing the âhavanîya fire and so on.--The assertion, again, made by the pûrvapakshin (Sûtra 46) that 'transference' strengthens his view in so far as transference is possible only where there is equality, is already refuted by the remark that also on our view transference is possible, since the fanciful fire-altars are equal to the real fire-altar in so far as both are fire-altars.--And that direct enunciation and so on favour our conclusion has been shown.--From connexion and so on it therefore follows that the agnis piled of mind, &c. are independent.--'As in the case of the separateness of other cognitions.' As other cognitions, such as e.g. the Sândilya-vidyâ, which have each their own particular connexion, separate themselves from works and other cognitions and are independent; so it is in our case also.--Moreover 'there is seen' an analogous case of independence from the leading subject-matter. The offering called aveshti which is mentioned in the sacred texts under the heading of the râgasûya-sacrifice, is to be taken out from that heading because it is connected with the three higher castes, while the râgasûya can be offered by a member of the warrior caste only. This has been explained in the first section (i.e. in the Pûrva Mîmâmsâ-sûtras).
265:1 Kimartham idam anubandhakaranam tad âha, sampad iti, upâstyartho hy anubandhas tathâpi manaskidâdînâm akriyâṅgatve kim âyâtam tad âha, na keti, teshâm kriyâṅgatve sâkshâd evâdhânâdiprasiddher anarthikâ sampad ity arthah. Ân. Gi.