The theory of non-duality is about the nature of reality within us and in all.
This theory is often referred to as the philosophy of Advaita Vedanta (the non dual understanding of the classic texts). It is closely connected with practical teachings on how to discover the abiding reality within ourselves, called Adhyatma Yoga (the way of Self-knowledge).
There is more about the connection between Advaita Vedanta and Adhyatma Yoga here.
The foundation of the non-dual teaching is that there is not more than one reality.
This seems logically clear and simple, yet the implications are far reaching.
It follows that reality is a non-dual whole, and that this is the reality in us, our own true Self.
So how does a world of diversity and change arise from oneness? And why do we think ourselves to be separate and vulnerable and feel that reality is unknown to us?
These are the questions addressed by the theory of non-duality.
It presents a view of the Self, of Reality, of God or the Absolute, and of the highest goal of inner enquiry.
Reality exceeds thoughts and words, so no statement of the theory can be entirely satisfactory. The teachings indicate to us the direction in which we are to look for ourselves.
The philosophy of Advaita Vedanta was brought to a high degree of completeness by the great philosopher-sage Shri Shankara, who lived around the 8th century CE. At Shanti Sadan we follow the tradition of Shri Shankara's school.
The theory of non-duality is rational and intellectually rigorous. But it is not intended to remain a purely intellectual matter, its purpose is to help us make the inner discovery for ourselves.