(9.2ab) The two truths are explained as conventional truths and ultimate truths.
Ultimate truth, emptiness, is a non-affirming negative phenomenon

Shantideva says emptiness is a non-affirming negative phenomena.  This explains the nature of the realization of emptiness itself. Here we need to use some technical terms, but I will try explain them in a simple and easy to understand way. The technical term is emptiness is a non-affirming negative phenomena. What does that mean? A negative phenomena is a phenomena that is realized by negating something else. For example, if I see the lack of money in my wallet, I realize that I am poor. The object of negation is money, I see it’s lack, and I realize that I am poor.  The lack of money is a negative phenomena.

A non-affirming negative phenomena is best understood by understanding what is an affirming phenomena. For example, if we say the fat man does not eat at night, then he must eat during the day. If someone grasps at gender binaries, and I say this person is not female, then we understand that the person is male. If I say in a coin toss it is not heads, then it implies that it is tails. These sorts of binaries are all examples of affirming negative phenomena. By negating one possibility, it necessarily implies the other possibility.

Emptiness, however, is a non-affirming negative. By negating its object, it does not affirm any other positive phenomena. It is simply the mere lack of something. The example that is traditionally given is space. Space is the lack of obstructive contact. The lack of obstructive contact does not imply or affirm any other phenomena. It is simply a mere lack of obstructive contact. This mere lack can have great meaning. For example, if I remember parking my car in space 24, and I then go to that space and see the mere lack of my car, this mere absence has great meaning. But it does not affirm any other positive phenomena. In the same way, emptiness is the mere lack of inherent existence, mere lack of existence from its own side, mere lack of independent existence, and so forth, but realizing this mere lack does not affirm any other phenomena. Nonetheless, it has great meaning. The meaning of emptiness is there is nothing to worry about, there is no one criticizing us, there is no death, no birth, and so forth. All of these things do not actually exist.

(9.2cd) That cannot be realized directly by a mind that has dualistic appearance,
For such minds are conventional, and thus mistaken awareness.

Once again Shantideva gives us some technical terms that we need to understand in order to grasp the meaning of emptiness that is presented. The first term is dualistic appearance. Dualistic appearance is when an object appears to be one with its inherent existence. Inherent existence is when we fail to see the difference between the basis of imputation and the imputation itself. We see the object itself as its basis. Dualistic appearance is when we see an object, we simultaneously see it as inherently existing or existing from its own side. Two things are appearing to our mind – the object itself and its inherent existence. This is dualistic appearance. The opposite of dualistic appearance is the union of appearance and emptiness. Here instead of the object appearing to be one with its inherent existence it appears to be one with its underlying emptiness. What we see is emptiness, but it appears as a form.

The second key term Shantideva refers to here is conventional appearance. A conventional appearance is something that we normally see, for example a car, a computer, or our best friend.  They are called conventional appearances because we all agree on the name to call these different objects. For example, when we see something with four wheels, a chassis, a motor, and seats, we call it a car. When we see a screen, a keyboard, and microchips, we call it a computer. The names car, computer, and so forth are the names we all agree by convention to call these specific objects with these particular functions. 

But fundamentally, conventional appearances are mistaken appearances. The things that we normally see appear to exist from their own side, independent of mind.  So while they appear, they do not in fact exist. Hence, they are mistaken. This can give rise to the question of whether Buddhas see conventional appearances. Does a Buddha see a car or a computer? If they don’t, how can we say they are omniscient? The answer is no, a Buddha does not see conventional appearances because conventional appearances are mistaken appearances and Buddhas only know truth.  Only emptiness is the truth. How can a Buddha see something that is not true?  So does that mean a Buddha only sees the clear light emptiness like a vast empty space? No, a Buddha does not just see the clear light emptiness. They do just see emptiness, but emptiness can appear in myriad different ways. Sometimes emptiness appears as a computer, sometimes it appears as a car, sometimes it appears as the clear light. Buddha sees only the infinite space of emptiness, but that emptiness appears in countless different ways. Therefore, Buddhas do see computers, cars, and so forth, they just don’t see the conventional appearances of computers, cars, and so forth that we normally see.  The things we normally see do not exist at all.

This can also give rise to the question of whether Buddhas see us seeing conventional appearances. The short answer is no, they do not. They see us as Buddhas seeing everything purely. They do not see us in this way because we objectively are Buddhas seeing things purely.  In fact, we are not objectively anything. Buddha’s see us seeing everything purely because this view functions to ripen us so that we are ourselves able to view things in this way. For ordinary beings they see suffering, and then engage in virtuous actions. For a Buddha, their pure view of us is their compassionate action. The duality between view an action has dissolved.

To keep it simple:  Ultimate truth is emptiness – that there is no thing that exists from its own side.  Conventional truth is things are nothing more than dream-like projections of mind.  If you look for something more than just a projection of mind, you find nothing.  Truth is relative.  Relative to conventional reality, a schizophrenic’s world is a mistaken appearance.  Relative to ultimate reality, conventional reality is a mistaken appearance.  Only emptiness is truth, but it can appear in countless ways.