Nonduality is a peculiar subject to write or to talk about. It concerns the ultimate nature of reality, and is therefore at the same time the most theoretical topic and the most tangible one, it is the most abstract because it deals with the absolute, which is by definition unattainable by our mind; but, since reality is all that exists, it is also the most concrete, covering every aspect of our life and of existence in general.
The non-dualistic vision defines reality as being one only and its manifestation as being unitary, that is, not producing any substantial separation within itself. In short, reality is a single system that includes all that exists and where there is no void, since everything is part of the same whole and is thus interconnected.
So far, the mind seems to accept these two fundamental principles without too much opposition. But they get more difficult to acknowledge when we consider our role within such a unitary system. In fact, however universal our idea of existence may be, the problem of how to reconcile our subjective experience of reality, that which we call “our life,” with the existence of a single entity that includes things that we have always considered instead as being different and separate, remains.
Just recently, scientists have affirmed that reality is not an objective entity we can relate to but is solely the subjective experience of existence. This is not an entirely new theory; we can find the same idea in the thousands of years-old Indian texts of the wisdom of Advaita, with the metaphor of the man who projects, or rather, superimposes upon a rope rolled up on the ground the image of a snake, from which he runs away scared, absolutely certain of the objectivity of his experience.
According to this interpretation, reality exists only as a projection of our mind on a single existing energy field. However, this plain statement is easily disputed, since reality existed before human beings evolved, will continue to exist after the disappearance of the last human being, and also exists where human beings are not present. So, let us stop considering the human being as core to the manifestation of reality and abandon the anthropocentric perspective underlying all research and reasoning about it, otherwise we will be unable to capture the essence of something that goes beyond every identification, every definition, and every measurement: the absolute one and universal reality.
This single entity, which is the sole existent, referred to in various traditions by different names (in the theistic traditions the Godhead, in non-theistic ones the Absolute or Universe), has therefore always existed—given that something cannot arise from nothing—and will exist forever because it cannot simply “disappear” into nothingness, the only accepted possibility being that it can instead somehow transform while maintaining its fundamental nature.
As regards its form, we can affirm that it coincides with its manifestation, which is in a state of perennial change at least in this phase of expansion, and that its main characteristic or quality is precisely this diversification. As a consequence, we can also affirm that the manifestation of reality is more abundant the more varying and diverse it is, and hence we can establish the following general principles: two are better than one, and two different are better than two equal.
As stated above, it is not easy to embrace the non-dualistic vision when our senses and intellect are constantly reinforcing our belief in duality and separation. Success will depend on our ability to discern whether our analysis of reality considers its nature or its manifestation. Basically, we need to be clear whether we are asserting the sameness of the nature of what we are considering with that of reality as a whole, or whether we are simply analyzing one of the infinite processes that reality manifests, to understand its characteristics. It is a difference equivalent to that of answers to the questions “what?” and “how?” Such clarity will help us to avoid the difficulties usually encountered in reconciling the multiplicity of the manifestation of reality with the oneness of its nature. In fact, as regards reality’s essence, there is no actual multiplicity to be brought back to unity since reality is only one; while with respect to differentiation in its manifestation, whatever we may consider is only one of the infinite ways it occurs.
In short, every analysis of reality must be consistent with the following principles:
- if we are considering its nature, it is non-dual, i.e. there is only one reality and therefore the nature or essence of all that exists is the same;
- if we are considering its manifestation, it is unitary, i.e. reality is a dynamic, ever-changing process that does not generate any substantial separation between its elements, and as a consequence there is no substantial separation to be brought back to unity.

Author's Bio: 

Eugenio Vignali for nearly forty years has studied Eastern and Western philosophies and sapiential traditions, focusing on nonduality in all its currents. He is the author of a book about the great Renaissance philosopher Nicholas of Cusa’s universal unity vision and of the book titled Understanding nonduality through color, where his unique method to develop a non-dualistic awareness is explained. He runs the blog, which is the largest online nonduality quotes database in Italian. He gives lectures, runs classes, and offers individual coaching sessions to learn the fundamentals about nonduality and how to make its intellectual understanding a true life-experience. More info in English at The book Understanding nonduality through color is available as epub on Google Books and Itunes Store.