Slightly off-topic: the logical justification for nonduality
Nonduality is the name of an understanding of reality that is arrived at in multiple ways both experiential and logical, but I would argue that it has the distinction of being a perspective that requires one to believe absolutely nothing that is not given directly in first-person experience. All other metaphysical positions come with some baggage that can never be proven, or even evidenced, in our experience. Nonduality proceeds directly from a standpoint of universal skepticism about all assumptions not given in our direct perception of life, whatever life may be. This post will give a (probably lengthy) account of the chain of reasoning that leads to the non-dual conclusion: that you alone are what actually exists, and you are just the simple awareness of your own existence.
We begin with the observation that, while we know that we exist beyond a shadow of a doubt, we can have all kinds of doubts about what we are. We seem to be a person with a body and a mind, but this may be an illusion, since we have the clear experience of believing ourselves to be a particular body and mind and being mistaken about that, such as when we are dreaming. Thus, the fact that it strongly seems as if we are a body with a mind is not evidence that we are actually a body/mind.
When do we seem to be a body/mind? In our experience, we seem to cycle through three distinct states. In our current state, the waking state, we seem to be individual beings with bodies and minds located in a world. In a very similar state, dreaming, we seem to be different bodies located in different worlds. But are these the only two states of being we know?
Importantly, there is a third state we experience: the state of dreamless sleep. In dreamless sleep, we have no awareness of a body, a mind, or a world, nor do we experience space and time. However, we are aware of our own existence, because when we leave the state of dreamless sleep, we clearly know that we were in a state with no awareness of any phenomena. Otherwise, we would experience an unbroken series of waking and dream states, and would have no concept of deep sleep; we would simply assume that for the entire time we slept, we were dreaming. We do not assume this, because we have clear introspective knowledge of having been in a state where no phenomena were present.
So, are we the bodies that we seem to be while waking or dreaming? If we were these bodies, then we would not be able to experience our own existence in their absence. Yet, while we are sleeping dreamlessly, we are aware of our existence while there is nothing else present, and certainly no body present.
If we exist and are aware of our existence in all three states, but seem to be a body in only two of the three, how can we assert that we are actually a body without accepting something we cannot experience directly? In our actual experience (in the uninterrupted awareness of our own existence), the phenomenon of seeming to be a body in a world rises and subsides. It rises in the waking state and the dream state alike, along with memories that create the impression of a continuous flow of time across multiple waking states.
Since we have the impression of continuity in both waking and dreams, there is no basis to conclude that the waking state is actually a continuous one while our dreams are intermittent and fleeting. The impression of continuity may certainly occur in a dream, where nothing exists independently of our perception of it. The same can be said of any justification we may provide in the waking state to establish it as primary or real relative to a dream.
In principle, there is no experience we can have in the waking state, when we are convinced that a world exists independently of our perception of it, that could not occur in a dream, when we have the same conviction even though it is known to have been mistaken when the dream ends.
Therefore, no evidence could possibly demonstrate that we are actually a body with a mind in an independently real waking world that exists even if we do not perceive it. As a result, the only reasonable conclusion is that the waking state is just a long dream, within which we seem to experience other dreams as well as dreamless sleep.
So, given all this, what are we?
The answer should be getting clearer now. We cannot be the bodies that appear in only two dreamlike states, since we clearly exist and are aware of our existence without the appearance of a body in the third state without dreams. We must therefore be whatever the appearance and disappearance of this erroneous body-identity occurs in. In our dreams, though we seem to be a dream character in a world of other characters, when we awaken we know none of them were real (not even the one we believed ourself to be). The same must therefore be true even of our waking experience, since as shown earlier, nothing experienced therein can unequivocally distinguish it from a dream. Taking ourself to be an individual in an independent world is a fundamental error.
What we actually are is formless, unlimited, infinite, and eternal awareness that is always aware of ourself, even when we seem to take the perspective of an individual (due to ignorance of our real nature) in the dream that is our life. But since dreams are unreal and do not really exist, the ultimate fact of the matter is that we have never actually made this mistake; we seem to undergo change while circulating through the three states, but in reality we are unchanging and do not have any state other than existing.
As a dream is nothing apart from the dreamer, and only exists in the view of the dreamer, the whole universe is your dream-projection (but not as the person you believe yourself to be; you are all the persons and the entire world). This is what non-duality, or advaita, means: other than you as unchanging awareness, there is no second thing, no countably separate reality; whatever seems to be separate from you is only an appearance that is made of you while appearing in you, which you mistake for something independent only when you take yourself to be an individual with a body.
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All of which is to say, this nonduality stuff is not the unfounded belief that we "don't exist" or "nothing is real". We exist and are real, and are in fact all that is real, but we are mistaken about what we are. Since we make this mistake whenever we know ourself as an individual with a body in a world, the reality of whatever we perceive is also mistaken. However, so long as we are under the sway of this delusion, and by all means I still am, we have no reason to behave as if this world is false. We should not use nonduality as justification for being cruel to others, since the only reason we would want to is because we feel someone else has something we want. If we are cruel, it is because we see the victim of our cruelty as separate from us, so nonduality can never justify cruelty.
On the contrary, knowing that everybody (or every body) including "yourself" is an appearance in a vast, unlimited awareness is an excellent reason to recede from egotistical behavior and practice compassion. What is worth pursuing in this world if it has no reality apart from you the pursuer? The sting of desiring this or fearing that becomes weaker and weaker as we progress on the non-dual path.
I will do my best to respond to any earnest questions while completely ignoring personal attacks or bad-faith remarks. Thanks for reading all this, if you in fact did read it all. :)