If no sentient being exists, for whom is there compassion? 'A Guide to the Bodhisattva Way of Life' by Santideva

Let me quote Dogen's Genjō Kōan:

When things are seen in context of Buddha-Dharma, there is "delusion vs enlightenment", "practice and study", "birth", "death", "Buddhas" and "sentient beings". When things are seen in context of Emptiness, there is no longer such thing as "delusion" and no "enlightenment", no Buddhas, no sentient beings, no birth, an no death.

The path to buddhahood starts with a feeling that there is "too much" of one thing and "not enough" of another, and in that context there are "birth" and "death", "delusion vs enlightenment", "ordinary beings" and "Buddhas". But in reality this feeling only comes from attachment to a certain perspective, just like when we get nostalgic over the blossoms’ withering but hate when the weeds are flowering.

To undertake the project of Enlightening the entire universe through one’s training while carrying the burden of self is a delusion. To have the entire Universe enlighten oneself through training is awakening. To have awaken to one’s delusion is to be enlightened -- and to be deluded about enlightenment is to be an ordinary being.

To take on your individual statements:

1) Sentient beings do not exist

Incorrect. From the perspective of someone who sees, things are beyond descriptions such as "sentient beings exist" or "sentient beings do not exist". The idea of "sentient beings" is but one way to describe reality.

2) For one to be compassionate he has to be deluded to believe that sentient beings exist.

Incorrect, "he" is not deluded, he's just able to understand the delusion of others. Empathy or compassion is an ability to imagine what the world looks like from another perspective. Because those who see the truth have such ability (as they attained the truth by completely and utterly letting go of their fixed perspective), they can see reality from a perspective of a description that uses the concept of "sentient beings" and all that goes with it. And when you see things from this perspective, you see suffering, birth, death etc. -- all that stuff exists from the same perspective.

3) Compassion itself is a delusion

Incorrect, compassion or empathy itself is a real skill. In cognitive science, being able to understand what the world looks like from another observer's standpoint is a key criteria of sentience.

4) One should remain deluded to alleviate the nonexisting suffering of nonexisting sentient beings.

Incorrect, to be able to understand different people and to ferry them across, one needs to be able to see reality beyond limitations of a single perspective, and to freely move between perspectives.

For others, what is just a mere delusion, is not a mere delusion, but reality.

For you, an enlightened being, there is no suffering, no sorrow, no pain, no happiness, no beings, no life, no death, no nothing, etc.

For others, not enlightened beings, there is suffering, sorrow, pain, happiness, beings, life, death, nothing, etc.

Because there actually is suffering, sorrow, pain, happiness, beings, life, death, nothing, etc. the Bodhisattva has compassion and it is the right thing to do because there actually IS suffering, sorrow, pain, happiness, etc.

UPDATE:

So you think everything is empty, thus there is nobody for whom to be compassionate. And now you're wondering if there is no object for compassion, then why compassion? For whom compassion, if there is nobody to be compassionate for?

The answer is in verse 75: "For one who is imagined through delusion". Thus, compassion is for nobody, but since this nobody actually IS somebody, that's why there is compassion for this somebody.

Even if a Bodhisattva knew that this somebody is actually nobody, he would still continue to be compassionate for this nobody because this nobody is deluded to be somebody. For nobody thinking he is somebody, there is suffering, sorrow, pain, happiness, beings, life, death, nothing, etc. and because for somebody there actually IS all this, this somebody is subjected to suffering. Even though there is nobody who suffers, there actually IS somebody due to him being deluded there is somebody and for him (the deluded one) there actually IS somebody who is suffering.

"For one who is imagined through delusion, which is accepted for the sake of the task." does not necessarily mean "For one to be compassionate he has to be deluded to believe that sentient beings exist". It can also mean "For one to be compassionate, other beings have to be deluded to believe that sentient beings exist".

In verses prior to verse 75 it says that the "I" cannot be found. Whenever the "I" is found, that is not the "I". Examples of this are here:

"73. The past or future mind is not "I," since it does not exist. If the present mind were "I," then when it had vanished, the "I" would not exist any more."

"74. Just as the trunk of a plantain tree is nothing when cut into pieces, in the same way, the "I" is non-existent when sought analytically."

To an uninstructed mind, it would logically follow that compassion is not needed, that's why this question arises:

[Qualm:] If no sentient being exists, for whom is there compassion?

And this is the answer:

[Madhyamika:] For one who is imagined through delusion, which is accepted for the sake of the task.

Given that the author in prior verses says that there actually is no "I" for whom to be compassionate, the only possible interpretation of the above answer can be this:

[Madhyamika:] For one who is imagined through delusion by the Bodhisattva or by the being, which is accepted as real by the Bodhisattva for the sake of the task.

If compassion would not be needed, there wouldn't be a long debate "why compassion is needed" and there wouldn't be the answer that compassion is needed for the one who is imagined through delusion. The "one who is imagined through delusion" does not cease to exist when the Bodhisattva eradicates his delusion nor when the being for which the Bodhisattva is compassionate eradicates his delusion. "one who is imagined through delusion" ceases when both the Bodhisattva and the being eradicate their delusions. When both eradicate their delusions, "one who is imagined through delusion" ceases to exist, there is no more suffering, no sorrow, no pain, no happiness, no beings, no life, no death, no nothing, etc., thus no more compassion is needed between the two because suffering actually ceases for both of them, comes to an end. Thus, until both eradicate their suffering, compassion is needed. As long as there will be deluded beings, compassion will be needed.

In the same way as verse 75, verse 76 can be interpreted.

The verse that follow then has sense:

77. However, grasping onto the "I," which is a cause of suffering, increases because of the delusion with regard to the Self. If this is the unavoidable result of that, meditation on identitylessness is the best.

I would interpret it like this:

77. However, grasping of the Bodhisattva onto the "I," which is a cause of suffering, increases because of the delusion with regard to the Self. If this is the unavoidable result of that, meditation on identitylessness is the best.

UPDATE 2:

You are indulging in the view "Sentient beings do not exist".

You think that sentient beings are just a dream. Thinking so, you think that once you wake up, sentient beings would vanish, because they haven't ever existed in the first place, isn't it? For you, sentient beings are non existent, isn't it? You think sentient beings are just characters in your dream, isn't it? You think that I and other sentient beings don't exist. That's what you think and that's the reason you're not satisfied with the answers.

You think that my dream is part of your dream. You think that my dream does not exist and that it's just part of your dream. That's not true. Your dream is your dream and my dream is my dream. They are two separate dreams. When you wake up from your dream, I'll still be in my dream. When you wake up from your dream, this world and the sentient beings in it would not cease to exist - they would still be in their dreams. But you, because you think that they are all part of your dream, think that they wouldn't exist anymore, which is incorrect.

Just think about all sentient beings who woke up from their dreams. If we were just a dream, after a sentient being woke up, then you and me would vanish and would not be here. But you and me are still here, even though numerous sentient beings woke up. How could that be?? They all woke up from their dreams, but we are still here? If we, sentient beings, were just a dream, we would vanish the moment a sentient being woke up. But that's not the case. We're still here, even though others woke up. Why we're still here?

Is it maybe because every sentient being is in his own dream? Yes, that is the answer.

Wrong view is: when I wake up from my dream, other sentient beings will stop dreaming because they haven't ever existed in the first place because they were just characters of my own dream.

Right view is: when I wake up from my dream, other sentient beings will continue to be in their dreams.

It is wrong view to say "Sentient beings do not exist". Right view is "Sentient beings neither do not exist nor exist" and even this view is wrong if not understood properly. Correct is to let go of all views:

"Does Master Gotama have any position at all?"

"A 'position,' Vaccha, is something that a Tathagata has done away with. What a Tathagata sees is this: 'Such is form, such its origination, such its disappearance; such is feeling, such its origination, such its disappearance; such is perception...such are fabrications...such is consciousness, such its origination, such its disappearance.' Because of this, I say, a Tathagata — with the ending, fading away, cessation, renunciation, & relinquishment of all construings, all excogitations, all I-making & mine-making & obsessions with conceit — is, through lack of clinging/sustenance, released."

Source: http://www.accesstoinsight.org/tipitaka/mn/mn.072.than.html

You are caught in a view "Sentient beings do not exist" which is one extreme:

"By & large, Kaccayana, this world is supported by (takes as its object) a polarity, that of existence & non-existence. But when one sees the origination of the world as it actually is with right discernment, 'non-existence' with reference to the world does not occur to one. When one sees the cessation of the world as it actually is with right discernment, 'existence' with reference to the world does not occur to one."

"'Everything exists': That is one extreme. 'Everything doesn't exist': That is a second extreme. Avoiding these two extremes, the Tathagata teaches the Dhamma via the middle

Source: http://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.015.than.html

You are caught in non-existence. You should let go of it and come out in the middle. It's because of the extreme "Sentient beings do not exist" that you can't see a reason for compassion.

The whole point of enlightenment is to avoid extremes and come in the middle.

Once you come in the middle, you will know that your dream is your dream and my dream is my dream, so even if you wake up from your dream, there will still be my dream. That's why compassion remains and that's the reason why compassion can continue to go on, even after awakening/enlightenment.