The following is an excerpt from The Center of the Sunlit Sky by Karl Brunnhölzl. This section is titled The Lineage of Vast Activity Is Not the Same as "Mere Mentalism" (Cittamatra), p. 471:
The lineage of vast activity denies any real or ultimate existence of "mere mind" (citta-matra) or "mere cognizance" (vijnapti-matra). For example, Asanga's Synopsis of Ascertainment refutes both "Sramanas and Brahmans who claim some substantially existing mere mind" by using reasoning and scripture. Vasubandhu's Commentary on The Distinction between the Middle and Extremes says:
"Based on the observation of mere cognizance, the nonobservation of [outer] referents arises. Based on the nonobservation of referents, also the nonobservation of mere cognizance arises. Thus, one engages in the characteristic of the nonexistence of both apprehender and apprehended. Therefore, observation is established as the nature of nonobservation, because if there is no referent to be observed, an observation [of it] it is not suitable. Thus, one should understand observation and nonobservation as being equal."
Sthiramati's subcommentary on this text elaborates:
"Thus, in its nature, observation is nonobservation.... [This means that] there is no difference between the nonobservation of referents and the observation as mere cognizance in that [both] do not exist. Thus, they are to be understood as equal.... [The latter] is just called "observation," since an unreal object appears [for it]. However, since there is no [actual] referent, nothing is observed by this ["observation"]. Therefore, ultimately, its nature is nonobservation.... Hence, it is said that it does not exist as the nature of observation. In such observation, neither is the nature of observation to be eliminated, nor is the nature of nonobservation to be established. They are the same in that they are undifferentiable.... "So why is [mere] cognition called 'observation' then?" In its nature, it is nonobservation, but [it is designated] in this way, since an unreal object appears [for it], as this is the convention in the world and the treatises."
Maitreya's Ornament of Sutras says:
"The mind is aware that nothing other than mind exists.
Then, it is realized that mind does not exist either.
The intelligent ones are aware that both do not exist
And abide in the expanse of dharmas (dharmadhatu) in which these are absent."
Even The Sutra of the Arrival in Lanka, which is so often considered one of the classic sutras of Mere Mentalism in the above sense, declares:
"Through reliance on mere mind,
One does not imagine outer objects.
By resting in the observed object of suchness,
One should go beyond mere mind too.
Going beyond mere mind,
One must even go beyond the nonappearance [of apprehender and apprehended].
The yogic practitioner who rests in nonappearance
Sees the great vehicle.
This spontaneously present, peaceful resting
Is completely purified through aspiration prayers.
Genuine identityless wisdom
Sees by way of nonappearance."
The same is clearly stated again and again in other texts of this tradition too, such as Maitreya's Distinction between Phenomena and Their Nature:
"Through [outer referents] being observed in this way, they are observed as mere cognizance.
Due to observing [them] as mere cognizance,
Referents are not observed,
And through not observing referents,
Mere cognizance is not observed [either].
Through not observing this [mere cognizance],
One enters into the observation of both being without difference.
This nonobservation of a difference between these two
Is nonconceptual wisdom.
It is without object and without observing,
Since it is characterized
By nonobservation of all characteristics."
Vasubandhu's Instruction on the Three Natures agrees:
"Through the observation of [objects] being merely mind,
A referent to be known is not observed.
Through not observing a referent to be known,
Mind cannot be observed [either].
Through not observing both,
The expanse of dharmas is observed."
His Thirty Verses says:
"When consciousness itself
Does not observe any observed object,
It rests in the actuality of mere consciousness (vijnaptimatrata),
Since there is no apprehender without something apprehended.
Being no-mind and nonreferential,
It is supramundane wisdom.
This is the complete change of state
And the relinquishment of the twofold impregnations of negativity.
It is the undefiled expanse
That is inconceivable, positive, and constant.
It is the blissful Body of Release
And the Dharma Body of the Great Sage."
In the gradual process of realizing true reality, the expedient purpose of the step of describing objects as being "merely mind" or "merely cognition" is to prevent the total denial of seeming reality in which subject and object appear. To start by presenting just the unqualified nonexistence of mind (the perceiving subject) courts the danger of falling into a nihilistic extreme by failing to account for the mere appearance of the interaction between mind and its objects. Such is stated in Sthiramati's Subcommentary on The Distinction between the Middle and Extremes:
"'[If neither objects nor mind exist,] then why is the nonexistence of mere cognizance not presented right from the start?' The apprehender depends on the apprehended. Consequently, if [it is established that] there is no object to be observed [by the apprehender], one may easily realize [the nonexistence of the apprehender too], since something that has the nature of being [its] observed object has been eliminated. Otherwise, existence would be altogether denied due to the lack of mutual dependence of apprehender and apprehended."
This does not differ from what Candrakirti's Entrance into Centrism says:
"The Buddhas said, "If there are no knowable objects,
One easily finds that a knower is excluded."
If knowable objects do not exist, the negation of a knower is established.
Therefore, they first negated knowable objects."
The lineage of vast activity clearly postulates that the actual liberating purpose of "mere mind" lies in going beyond it, that is, transcending duality by pointing beyond this very mind and entering the middle path of emptiness or suchness. In this, The Sutra of the Arrival in Lanka is followed:
"The [Buddhas] do not see mere mind.
Since there is nothing to be seen [by it], it does not arise.
This middle path is what is taught
By me as well as by others.
Arising and nonarising
As well as entities and nonentities are emptiness.
The lack of nature of [all] entities
Is not to be conceived in terms of such pairs.
Through the realization that what is seen is of one's own mind,
Clinging to duality is abandoned.
Abandoning means fully understanding
And not destroying mind's imagining activity.
Through the full understanding that what is seen is of one's own mind,
Mind's imagining activity ceases to operate.
Since mind's imagining activity ceases to operate,
Suchness has become free from mind."
From all of these sources, it should be very clear that such Yogacara terms as "mere mind," "mere cognizance," and "mere consciousness" are used in describing a meditative progression or as provisional antidotes for clinging to external referents. However, these notions are in no way ontologically or metaphysically reified. Rather, once their purpose is fulfilled—that is, realizing that both apprehender and apprehended do not really exist—they are put out of commission. The notion of "mere mind" in Yogacara is as self-negating as the notion of emptiness in Centrism. Just as in the case of emptiness, to reify or cling to the antidote only turns it into poison.